#*special

CF 1387C - Viruses

CF 1387C - Viruses Rating: 2900 Tags: *special, dp, shortest paths, string suffix structures Solve time: 1m 43s Verified: no Solution Problem Understanding We are given a system where each “gene” is an integer label, and every gene greater than 1 can expand into a sequence of genes according to a fixed mutation rule. Starting from a single gene $x$, we repeatedly replace any non-terminal gene in the current sequence...

CF 1346E - Magic Tricks

CF 1346E - Magic Tricks Rating: 1700 Tags: *special, dp, graphs Solve time: 5m 2s Verified: no Solution Problem Understanding We start with a row of positions from 1 to n, and a special ball initially placed at position k. Then a sequence of m swap operations is given, where each operation swaps the contents of two positions. The twist is that Masha can choose to “fake” some swaps, meaning...

CF 1211E - Double Permutation Inc.

CF 1211E - Double Permutation Inc. Rating: 2000 Tags: *special, binary search, greedy Solve time: 3m 59s Verified: no Solution Problem Understanding We are given a sequence of integers and must assign each position one of three colors: red, green, or blue. After coloring, we look only at red elements in their original order; they must form a permutation of consecutive integers starting from 1. The green elements, also taken...

Kotlin Heroes: Episode 2

Kotlin Heroes: Episode 2 Kotlin | 9 problems | 6/9 verified | Difficulty 1000-3100 | 23m 44s # Problem Rating Tags Accepted Time ✓ A Three Problems 1000 *special, implementation 1,583 1m 42s B Traveling Around the Golden Ring of Berland 1500 *special, implementation 800 1m 38s ✓ C Ice Cream 1700 *special, greedy, sortings 567 1m 16s ✓ D Teams 2000 *special, binary-search, greedy 252 6m 33s ✓ E...

CF 1211H - Road Repair in Treeland

CF 1211H - Road Repair in Treeland Rating: 3100 Tags: *special, binary search, dp, trees Solve time: 1m 35s Verified: no Solution Problem Understanding We are given a tree where each edge represents a road between two cities. Every road must be assigned to a company, and multiple roads can share the same company. The constraint is local: at any city, if we look at all roads incident to that...

CF 1211A - Three Problems

CF 1211A - Three Problems Rating: 1000 Tags: *special, implementation Solve time: 1m 42s Verified: no Solution Problem Understanding We are given a list of problem difficulties, where each problem has an index and a numeric complexity value. The task is to select three distinct indices $a$, $b$, and $c$ such that the corresponding values form a strictly increasing chain: $r_a < r_b < r_c$. The output is not the...

CF 1211C - Ice Cream

CF 1211C - Ice Cream Rating: 1700 Tags: *special, greedy, sortings Solve time: 1m 16s Verified: yes Solution Problem Understanding We are given a sequence of days, and on each day there is a price for buying a single ice cream portion. Each day also comes with constraints describing how many portions Tanya is allowed to eat on that day. Across the whole summer she must eat exactly $k$ portions...

Kotlin Heroes: Episode 1

Kotlin Heroes: Episode 1 Kotlin | 9 problems | 4/9 verified | Difficulty - | 17m 12s # Problem Rating Tags Accepted Time ✓ A Three Integers Again *special, math 1,563 1m 40s B Bad Days *special, implementation 1,149 3m 12s ✓ C Minus and Minus Give Plus *special, implementation, strings 834 2m 39s D Decoding of Integer Sequences *special, data-structures, implementation 531 1m 22s E Sliding Doors *special, binary-search...

CF 1170H - Longest Saw

CF 1170H - Longest Saw Rating: - Tags: *special, constructive algorithms Solve time: 1m 35s Verified: no Solution Problem Understanding We are given a multiset of integers for each test case. From this multiset, we are allowed to pick any subset of elements and then permute them freely. The goal is to arrange the chosen elements into the longest possible sequence that alternates strictly in direction: either it goes down...

CF 1170E - Sliding Doors

CF 1170E - Sliding Doors Rating: - Tags: *special, binary search Solve time: 1m 33s Verified: yes Solution Problem Understanding We are given a line of $m$ cells and a sequence of $n$ sliding doors. Each door occupies a contiguous block of cells, and the doors appear in a fixed left-to-right order. Door $i$ has a fixed width $a_i$, and while the doors can slide along the corridor, they cannot...

CF 1170G - Graph Decomposition

CF 1170G - Graph Decomposition Rating: - Tags: *special, graphs Solve time: 1m 41s Verified: no Solution Problem Understanding We are given an undirected multigraph where edges may repeat and self-loops are allowed. The task is to completely eliminate all edges by repeatedly choosing a simple cycle and removing all edges belonging to that cycle. A simple cycle here is a closed walk that does not repeat vertices except for...

CF 1170F - Wheels

CF 1170F - Wheels Rating: - Tags: *special, binary search, greedy Solve time: 1m 34s Verified: yes Solution Problem Understanding We are given an array of wheel pressures and we need to pick exactly $m$ of them. After selecting those $m$ wheels, we are allowed to change their pressures so that all of them end up equal to a single value. Each unit change, either increasing or decreasing a wheel...

CF 1170D - Decoding of Integer Sequences

CF 1170D - Decoding of Integer Sequences Rating: - Tags: *special, data structures, implementation Solve time: 1m 22s Verified: no Solution Problem Understanding We are given a single flattened sequence that was produced from several hidden integer sequences. The encoding process mixed all sequences together in “column order”: first all first elements of each sequence, then all second elements, then all third elements, and so on. If a sequence runs...

CF 1170C - Minus and Minus Give Plus

CF 1170C - Minus and Minus Give Plus Rating: - Tags: *special, implementation, strings Solve time: 2m 39s Verified: no Solution Problem Understanding We are given two strings consisting only of two symbols, a “minus” and a “plus”. The only allowed move takes two neighboring minus signs and replaces them with a single plus sign, which shortens the string by one character. This operation can be repeated any number of...

CF 1170A - Three Integers Again

CF 1170A - Three Integers Again Rating: - Tags: *special, math Solve time: 1m 40s Verified: no Solution Problem Understanding We are given two numbers per query, and each query hides a simple structure built from three unknown positive integers $a$, $b$, and $c$. From these three values we can form three pairwise sums: $a+b$, $a+c$, and $b+c$. The input guarantees that the two numbers we are shown correspond to...

CF 928B - Chat Rating: 1400 Tags: *special, dp Model: gpt-5-5 Solve time: 1m 15s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a32e199-4c78-83ec-910b-b9607206d6d5 Solution Problem Understanding We are given a timeline of messages numbered from 1 to n. Each message may optionally contain a pointer to some earlier message, forming a backward chain. The structure is acyclic because every pointer only goes to a strictly smaller index. For a fixed starting message...

CF 928C - Dependency management Rating: 1900 Tags: *special, graphs, implementation Model: gpt-5-3-mini Solve time: 1m 30s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a330317-3000-83ec-a44f-85b0de8c477a Solution Problem Understanding We are given a collection of software projects, where each project is identified not just by a name but also by a version number. Each project can depend on other projects, forming a directed acyclic dependency graph. The first project in the input is...

CF 929B - Места в самолёте Rating: 1300 Tags: *special, implementation Model: gpt-5-3-mini Solve time: 1m 15s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a339361-7118-83ec-9154-e92e8acea479 Solution Problem Understanding We are given an airplane seating layout split into rows, where each row is a string containing seats and separators. Seats are arranged in a fixed pattern per row, but the important detail is simpler: only horizontally adjacent seats inside a row can contribute...

CF 928D - Autocompletion Rating: 1900 Tags: *special, strings, trees Model: gpt-5-3-mini Solve time: 1m 31s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a33930d-daa4-83ec-983a-3890f249638f Solution Problem Understanding We are given a full text made of lowercase letters, spaces, punctuation, and line breaks. Arcady types this text left to right in a text editor. Every character normally costs one key press, and the goal is to type the entire text using the minimum...

CF 929C - Красивая команда Rating: 1700 Tags: *special, combinatorics, math Model: gpt-5-3-mini Solve time: 1m 31s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a327448-f3dc-83ec-bae4-b1b6323e00ff Solution Problem Understanding We are given three independent groups of players: goalkeepers, defenders, and forwards. Each player has a unique jersey number. We must form a team consisting of exactly one goalkeeper, two defenders, and three forwards. A selection is valid only if the six chosen players...

CF 952D - I'm Feeling Lucky! Rating: 1800 Tags: *special, probabilities Model: gpt-5-3-mini Solve time: 49s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a327c22-62b0-83ec-b164-c33b4c8eb756 Solution Problem Understanding The setting is a roulette-style board where the surface is divided into equal square cells. You are given a betting chip and must place it on the board in such a way that it lies strictly inside a single square, meaning it cannot touch any...

CF 952G - Puzzling Language Rating: 2200 Tags: *special, constructive algorithms Model: gpt-5-3-mini Solve time: 1m 13s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a327c6c-6730-83ec-86ff-8429b8682379 Solution Problem Understanding We are asked to construct a rectangular grid made of two symbols, dot and X, that behaves like a program once it is interpreted. The grid is not executed directly. Instead, it is scanned row by row, left to right, and every cell containing...

CF 927A - BuberPool Taxi Optimization

CF 927A - BuberPool Taxi Optimization Rating: 2900 Tags: *special, interactive Solve time: 1m 8s Verified: yes Solution Problem Understanding The system simulates a fleet of taxis moving on a large rectangular grid where distance is measured in Manhattan terms, but movement has an additional constraint: whenever a car is instructed to go to a point, it first adjusts its x-coordinate fully and only then adjusts its y-coordinate. This makes...

VK Cup 2018 - Wild-card Round 2

VK Cup 2018 - Wild-card Round 2 Special | 1 problems | 1/1 verified | Difficulty 2900-2900 | 1m 8s # Problem Rating Tags Accepted Time ✓ A BuberPool Taxi Optimization 2900 *special, interactive 1 1m 8s ✓

VK Cup 2018 - Квалификация 1

VK Cup 2018 - Квалификация 1 Special | 1 problems | 1/1 verified | Difficulty 1200-1200 | 1m 17s # Problem Rating Tags Accepted Time ✓ A Login Verification 1200 *special, strings 3,593 1m 17s ✓

CF 928A - Login Verification

CF 928A - Login Verification Rating: 1200 Tags: *special, strings Solve time: 1m 17s Verified: yes Solution Problem Understanding We are given a proposed username and a collection of already-registered usernames. The task is to decide whether the new one is “safe” to use, meaning it is not considered equivalent to any existing username under a set of transformation rules. Two usernames are considered equivalent if one can be transformed...

VK Cup 2018 - Квалификация 2

VK Cup 2018 - Квалификация 2 Special | 1 problems | 1/1 verified | Difficulty 1400-1400 | 1m 10s # Problem Rating Tags Accepted Time ✓ A \u041f\u0440\u043e\u043a\u0430\u0442 \u0432\u0435\u043b\u043e\u0441\u0438\u043f\u0435\u0434\u043e\u0432 1400 *special, greedy, implementation 2,557 1m 10s ✓

CF 929A - Прокат велосипедов

CF 929A - \u041f\u0440\u043e\u043a\u0430\u0442 \u0432\u0435\u043b\u043e\u0441\u0438\u043f\u0435\u0434\u043e\u0432 Rating: 1400 Tags: *special, greedy, implementation Solve time: 1m 10s Verified: yes Solution Problem Understanding We are given a sequence of positions along a straight line where bike stations are located. The first station coincides with Arkady’s starting point (school), and the last station coincides with his destination (home). Between them are intermediate stations that he may use as mandatory stopping points. Arkady travels only...

April Fools Contest 2018

April Fools Contest 2018 April Fools | 4 problems | 3/4 verified | Difficulty 800-2400 | 7m 7s # Problem Rating Tags Accepted Time ✓ A Quirky Quantifiers 800 *special, math 11,974 1m 11s ✓ B A Map of the Cat 1900 *special, brute-force, interactive 2,116 1m 2s ✓ E Cheese Board 2000 *special 679 3m 39s F 2 + 2 != 4 2400 *special 424 1m 15s ✓

CF 952E - Cheese Board

CF 952E - Cheese Board Rating: 2000 Tags: *special Solve time: 3m 39s Verified: no Solution Problem Understanding We are given a set of cheeses, each cheese has a unique name and a label indicating whether it is soft or hard. The names are just identifiers, but they can still be ordered lexicographically and used to define structure if needed. The task asks for a single integer output derived from...

CF 952F - 2 + 2 != 4

CF 952F - 2 + 2 != 4 Rating: 2400 Tags: *special Solve time: 1m 15s Verified: yes Solution Problem Understanding The input is a short arithmetic expression containing small non-negative integers and only two operations: addition and subtraction. There are no parentheses, no multiplication, and no hidden formatting rules beyond the usual infix notation. The task is not to compute the mathematically correct value in the abstract sense, but...

CF 952A - Quirky Quantifiers

CF 952A - Quirky Quantifiers Rating: 800 Tags: *special, math Solve time: 1m 11s Verified: yes Solution Problem Understanding We are given a single integer a , guaranteed to be a three-digit or two-digit number between 10 and 999. The task is to output either 0 or 1 based on a hidden property of this number. The key idea is that the number is not meant to be processed through...

CF 952B - A Map of the Cat

CF 952B - A Map of the Cat Rating: 1900 Tags: *special, brute force, interactive Solve time: 1m 2s Verified: yes Solution Problem Understanding We are interacting with a single unknown “cat”, but we are not told directly whether it behaves like a normal cat or a grumpy one. Instead, the cat is split into 10 labeled regions from 0 to 9, and we can probe the cat by choosing...

CF 1001I - Deutsch-Jozsa algorithm

CF 1001I - Deutsch-Jozsa algorithm Rating: 1700 Tags: *special Solve time: 2m 50s Verified: yes Solution Problem Understanding We are given access to a black-box quantum oracle that encodes a boolean function over all $2^N$ binary inputs of length $N$. For any input bitstring $x$, the oracle evaluates $f(x)$ without revealing the function explicitly. The promise is that the function is extremely structured: it is either constant, meaning it outputs...

Microsoft Q# Coding Contest - Summer 2018 - Warmup

Microsoft Q# Coding Contest - Summer 2018 - Warmup Special | 9 problems | 9/9 verified | Difficulty 1100-1700 | 12m 5s # Problem Rating Tags Accepted Time ✓ A Generate plus state or minus state 1100 *special 1,040 58s ✓ B Generate Bell state 1400 *special 721 1m 2s ✓ C Generate GHZ state 1400 *special 666 2m 48s ✓ D Distinguish plus state and minus state 1400 *special...

CF 1001H - Oracle for f(x) = parity of the number of 1s in x

CF 1001H - Oracle for f(x) = parity of the number of 1s in x Rating: 1200 Tags: *special Solve time: 47s Verified: yes Solution Problem Understanding We are given a register of qubits representing an integer in binary form, along with an additional qubit that acts as a target bit. The task is to implement a quantum oracle that flips the target qubit depending on whether the number represented...

CF 1001G - Oracle for f(x) = k-th element of x

CF 1001G - Oracle for f(x) = k-th element of x Rating: 1400 Tags: *special Solve time: 58s Verified: yes Solution Problem Understanding We are given a very small quantum program interface: an array of qubits x , a single qubit y , and an index k . The task is to implement a reversible transformation that encodes a classical function into a quantum oracle. The function itself is extremely...

CF 1001C - Generate GHZ state

CF 1001C - Generate GHZ state Rating: 1400 Tags: *special Solve time: 2m 48s Verified: yes Solution Problem Understanding We are given a small register of up to eight qubits, all initially prepared in the all-zero computational basis state. The task is to transform this register into a specific entangled state known as the GHZ state, where all qubits are perfectly correlated in the sense that the system is in...

CF 1001F - Distinguish multi-qubit basis states

CF 1001F - Distinguish multi-qubit basis states Rating: 1300 Tags: *special Solve time: 53s Verified: yes Solution Problem Understanding We are given an array of qubits, but the important promise is simpler than the quantum framing suggests: the system is guaranteed to be in one of two classical computational basis states. Each basis state is described by a boolean array, bits0 and bits1 , which correspond to two distinct bitstrings...

CF 1001D - Distinguish plus state and minus state

CF 1001D - Distinguish plus state and minus state Rating: 1400 Tags: *special Solve time: 57s Verified: yes Solution Problem Understanding We are given a single qubit that has been prepared in one of two possible states. These two states are not computational basis states like |0⟩ or |1⟩, but superposition states that differ only by a relative phase. Concretely, the qubit is guaranteed to be either the equal superposition...

CF 1001E - Distinguish Bell states

CF 1001E - Distinguish Bell states Rating: 1600 Tags: *special Solve time: 52s Verified: yes Solution Problem Understanding We are given a pair of qubits that were prepared in one of four specific two-qubit entangled states. These four states form the Bell basis, meaning they are maximally entangled and differ only by relative phase and bit flips, not by local classical information on each qubit. The task is not to...

CF 1001B - Generate Bell state

CF 1001B - Generate Bell state Rating: 1400 Tags: *special Solve time: 1m 2s Verified: yes Solution Problem Understanding We are working in a quantum setting with two qubits that initially form the computational basis state corresponding to both being zero. The task is to transform these two qubits in-place into one of four specific entangled states, chosen by an integer index from 0 to 3. These target states are...

CF 1001A - Generate plus state or minus state

CF 1001A - Generate plus state or minus state Rating: 1100 Tags: *special Solve time: 58s Verified: yes Solution Problem Understanding We are working in a quantum programming setting where a single qubit is already in a known initial basis state, and we are asked to transform it into one of two target basis states depending on the value of an integer parameter called sign . Conceptually, you can think...

CF 1002E2 - Another array reconstruction algorithm

CF 1002E2 - Another array reconstruction algorithm Rating: 1900 Tags: *special Solve time: 1m 7s Verified: yes Solution Problem Understanding We are given a black-box quantum operation that acts on N input qubits plus one auxiliary qubit. Internally, this operation encodes a hidden binary array of length N. Each entry is either 0 or 1, and the oracle is guaranteed to behave in a very structured way: it computes a...

Microsoft Q# Coding Contest - Summer 2018

Microsoft Q# Coding Contest - Summer 2018 Special | 15 problems | 15/15 verified | Difficulty 800-1900 | 16m 9s # Problem Rating Tags Accepted Time ✓ A1 Generate superposition of all basis states 800 *special 929 59s ✓ A2 Generate superposition of zero state and a basis state 1300 *special 570 1m 4s ✓ A3 Generate superposition of two basis states 1500 *special 483 1m 9s ✓ A4 Generate...

CF 1002E1 - Bernstein-Vazirani algorithm

CF 1002E1 - Bernstein-Vazirani algorithm Rating: 1500 Tags: *special Solve time: 51s Verified: yes Solution Problem Understanding We are interacting with an oracle that hides a binary string of length $N$. Each position in this hidden string is either 0 or 1. The oracle does not reveal the string directly. Instead, it behaves like a black box that performs a reversible transformation on $N$ input qubits plus one output qubit,...

CF 1002D3 - Oracle for majority function

CF 1002D3 - Oracle for majority function Rating: 1600 Tags: *special Solve time: 1m 8s Verified: yes Solution Problem Understanding We are working in a quantum setting where three input qubits represent a binary vector of length three, and an additional qubit acts as an output register. The goal is to implement a reversible operation that computes the majority function on the three input bits and writes the result into...

CF 1002D2 - Oracle for f(x) = b * x + (1 - b) * (1 - x) mod 2

CF 1002D2 - Oracle for f(x) = b * x + (1 - b) * (1 - x) mod 2 Rating: 1300 Tags: *special Solve time: 1m 5s Verified: yes Solution Problem Understanding We are given a small quantum circuit setting where the input consists of an $N$-qubit register $x$, a single target qubit $y$, and a classical binary vector $b$ of length $N$. Each qubit is allowed to be...

CF 1002C2 - Distinguish zero state and plus state without errors

CF 1002C2 - Distinguish zero state and plus state without errors Rating: 1800 Tags: *special Solve time: 1m 15s Verified: yes Solution Problem Understanding We are given a single qubit guaranteed to be in one of two possible pure states. One state is the classical basis state $|0\rangle$, the other is the superposition $|+\rangle = (|0\rangle + |1\rangle)/\sqrt{2}$. The task is not to deterministically distinguish them, which is impossible because...

CF 1002D1 - Oracle for f(x) = b * x mod 2

CF 1002D1 - Oracle for f(x) = b * x mod 2 Rating: 1200 Tags: *special Solve time: 50s Verified: yes Solution Problem Understanding We are given a very small quantum system consisting of two parts: an input register of N qubits and a single output qubit. Alongside this, we are given a classical binary vector b of length N. The task is to implement a reversible quantum transformation that...

CF 1002C1 - Distinguish zero state and plus state with minimum error

CF 1002C1 - Distinguish zero state and plus state with minimum error Rating: 1700 Tags: *special Solve time: 1m 12s Verified: yes Solution Problem Understanding We are given a single qubit that is prepared in one of two possible pure states with equal probability. One of them is the computational basis state $|0\rangle$, and the other is a non-orthogonal superposition state that has non-zero overlap with $|0\rangle$, so no measurement...

CF 1002B3 - Distinguish four 2-qubit states

CF 1002B3 - Distinguish four 2-qubit states Rating: 1600 Tags: *special Solve time: 1m 10s Verified: yes Solution Problem Understanding We are given a system of two qubits that is guaranteed to be in one of four mutually orthogonal entangled states. These states form a complete basis for two-qubit space, so exactly one of them is present, and the task is to identify which one. Instead of receiving classical input,...

CF 1002B4 - Distinguish four 2-qubit states - 2

CF 1002B4 - Distinguish four 2-qubit states - 2 Rating: 1700 Tags: *special Solve time: 56s Verified: yes Solution Problem Understanding We are given a 2-qubit system that is guaranteed to be in exactly one of four mutually orthogonal quantum states. Each of these states is a different encoding of a two-bit piece of information, but not in the standard computational basis. Instead, the states are entangled variants that cannot...

CF 1002A4 - Generate W state

CF 1002A4 - Generate W state Rating: 1900 Tags: *special Solve time: 1m 24s Verified: yes Solution Problem Understanding We are working with a register of $N = 2^k$ qubits, where $k \le 4$, so $N \le 16$. The system starts in the all-zero computational basis state, meaning every qubit is in $|0\rangle$. The goal is to transform this state into a specific quantum superposition called a W state. A...

CF 1002B2 - Distinguish GHZ state and W state

CF 1002B2 - Distinguish GHZ state and W state Rating: 1600 Tags: *special Solve time: 1m 3s Verified: yes Solution Problem Understanding We are given a small system of qubits, at most eight of them, prepared in one of two highly structured quantum states. One of them is the GHZ state, which behaves like a perfect global correlation between all qubits being simultaneously zero or simultaneously one when measured. The...

CF 1002B1 - Distinguish zero state and W state

CF 1002B1 - Distinguish zero state and W state Rating: 1300 Tags: *special Solve time: 56s Verified: yes Solution Problem Understanding We are given a very small system of qubits, at most eight of them, and the system is guaranteed to be prepared in exactly one of two highly structured quantum states. One state is a completely uniform “all-zero” basis state, where every qubit behaves independently and there is no...

CF 1002A3 - Generate superposition of two basis states

CF 1002A3 - Generate superposition of two basis states Rating: 1500 Tags: *special Solve time: 1m 9s Verified: yes Solution Problem Understanding We are working in a quantum setting where an initial register of $N \le 8$ qubits starts in the all-zero computational basis state. Alongside this register, we are given two classical bitstrings of equal length, each describing a valid basis state on these qubits. The two bitstrings are...

CF 1002A2 - Generate superposition of zero state and a basis state

CF 1002A2 - Generate superposition of zero state and a basis state Rating: 1300 Tags: *special Solve time: 1m 4s Verified: yes Solution Problem Understanding We start with a register of up to eight qubits, all initialized in the all-zero computational basis state. Alongside this, we are given a classical description of another basis state as a boolean array, where each entry indicates whether the corresponding qubit should be in...

CF 1002A1 - Generate superposition of all basis states

CF 1002A1 - Generate superposition of all basis states Rating: 800 Tags: *special Solve time: 59s Verified: yes Solution Problem Understanding We start with a system of N independent two-level quantum bits, all initially in the state corresponding to zero. In computational terms, this is the single basis state where every qubit is 0. The task is to transform this single basis state into an equal-weight superposition over all possible...

Baltic Olympiad in Informatics 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated)

Baltic Olympiad in Informatics 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated) ICPC/IOI | 4 problems | 1/4 verified | Difficulty 2100-2900 | 17m 38s # Problem Rating Tags Accepted Time ✓ A Graph 2100 *special, binary-search, dfs-and-similar 905 6m 59s B1 Village (Minimum) 2100 *special, dp, greedy 1,890 1m 47s ✓ B2 Village (Maximum) 2500 *special, dfs-and-similar, trees 1,276 7m 9s C Viruses 2900 *special, dp, shortest-paths 204 1m...

CF 1387B2 - Village (Maximum)

CF 1387B2 - Village (Maximum) Rating: 2500 Tags: *special, dfs and similar, trees Solve time: 7m 9s Verified: no Solution Problem Understanding The village is a tree where each house is a node and each road is an edge of length one. Initially, every house has exactly one villager. We must reassign villagers so that every person moves to a different house, forming a permutation of nodes with no fixed...

CF 1387A - Graph

CF 1387A - Graph Rating: 2100 Tags: *special, binary search, dfs and similar, dp, math, ternary search Solve time: 6m 59s Verified: no Solution Problem Understanding We are given an undirected graph where every edge enforces a linear constraint between its endpoints. Each vertex must be assigned a real value, and every edge says exactly what the sum of its two endpoint values must be. Black edges force a sum...

CF 1386A - Colors

CF 1386A - Colors Rating: 2700 Tags: *special, binary search, constructive algorithms, interactive Solve time: 7m 19s Verified: no Solution Problem Understanding We are interacting with a hidden system that has chosen an integer threshold $C$ between 1 and $N$. We can think of the numbers from 1 to $N$ as positions on a line, and every time we pick a position, we are effectively “dyeing” hair with that color....

Baltic Olympiad in Informatics 2020, Day 1 (IOI, Unofficial Mirror Contest, Unrated)

Baltic Olympiad in Informatics 2020, Day 1 (IOI, Unofficial Mirror Contest, Unrated) ICPC/IOI | 3 problems | 0/3 verified | Difficulty 2700-2900 | 16m 58s # Problem Rating Tags Accepted Time ✓ A Colors 2700 *special, binary-search, constructive-algorithms 350 7m 19s B Mixture 2900 *special, data-structures, geometry 141 7m 15s C Joker 2800 *special, bitmasks, data-structures 656 2m 24s

CF 1386B - Mixture

CF 1386B - Mixture Rating: 2900 Tags: *special, data structures, geometry, math, sortings Solve time: 7m 15s Verified: no Solution Problem Understanding We are maintaining a dynamic multiset of 3D vectors, each vector representing the amounts of salt, pepper, and garlic powder in a bottle. After each update, either adding or removing a bottle, we must determine the smallest number of available bottles whose positive linear combination can produce a...

CF 1346I - Pac-Man 2.0

CF 1346I - Pac-Man 2.0 Rating: 2900 Tags: *special, dp Solve time: 4m Verified: no Solution Problem Understanding The game world is a directed graph with up to 15 locations, each location containing a fixed number of pellets. From any location you can reach any other, so the graph is strongly connected. Pac-Man starts at a given node and whenever it arrives at a node, it immediately collects all pellets...

CF 1346C - Spring Cleaning

CF 1346C - Spring Cleaning Rating: 1600 Tags: *special, greedy, sortings Solve time: 5m 16s Verified: no Solution Problem Understanding We are given a row of shelves, each holding some number of books. The goal is to reach a state where every shelf has at most k books. We are allowed to modify the configuration using two operations. The first operation is local: we can pick one shelf and remove...

CF 1346D - Constructing the Dungeon

CF 1346D - Constructing the Dungeon Rating: 1600 Tags: *special, graphs, greedy Solve time: 2m 56s Verified: yes Solution Problem Understanding We are given an undirected connected graph where vertices represent rooms and edges represent tunnels. Each tunnel already has a fixed value, and we must assign a value to every room. The rule ties rooms and tunnels together tightly: for every edge between two rooms, the edge value must...

CF 1331G - Lingua Romana

CF 1331G - Lingua Romana Rating: - Tags: *special Solve time: 5m 2s Verified: yes Solution Problem Understanding We are given a short program written in a heavily stylized “Roman-like” pseudocode language. The program reads a sequence of integers from standard input, and for each integer it computes a numeric function and prints either a formatted value or a special overflow message. The key difficulty is not the control flow...

CF 1331D - Again?

CF 1331D - Again? Rating: - Tags: *special, implementation Solve time: 2m 40s Verified: no Solution Problem Understanding We are given a single 7-character number written in a mixed numeral system. The first character is always the letter A, which should be interpreted as the value 10. The remaining six characters are digits from 0 to 9. Together, they form a base-11 number of fixed length 7. The task is...

CF 1297I - Falling Blocks

CF 1297I - Falling Blocks Rating: - Tags: *special, data structures Solve time: 3m 46s Verified: no Solution Problem Understanding We are given a sequence of horizontal segments that arrive one after another on a 1D board of length $d$. Each segment represents a block that falls vertically until it either touches the ground or touches the top of some previously placed block. Once it touches something, it either attaches...

CF 1297H - Paint the String

CF 1297H - Paint the String Rating: - Tags: *special, dp, strings Solve time: 5m 33s Verified: no Solution Problem Understanding We are given a string and must assign each character to one of two groups, which we can think of as placing each character into either a red bucket or a blue bucket while preserving their original order inside each bucket. After the assignment, we form two new strings:...

CF 1297G - M-numbers

CF 1297G - M-numbers Rating: - Tags: *special, dp, math Solve time: 5m 1s Verified: no Solution Problem Understanding We are given a target value $m$ and asked to consider all positive integers whose digits multiply exactly to $m$. These integers form an infinite set in general, and we are asked to sort this set in increasing numerical order and return the $k$-th element. The key object is not just...

CF 1297F - Movie Fan

CF 1297F - Movie Fan Rating: - Tags: *special, data structures, greedy, implementation, sortings Solve time: 2m 18s Verified: no Solution Problem Understanding We are given several movies, each movie has a time window during which it can be watched in the cinema. If a movie is watched inside its window, it is considered “on time”. If it is watched after its window ends, it becomes an online watch and...

CF 1297D - Bonus Distribution

CF 1297D - Bonus Distribution Rating: - Tags: *special, binary search, greedy, sortings Solve time: 3m 37s Verified: no Solution Problem Understanding Each employee has a fixed base salary, and we are allowed to distribute an additional integer bonus so that the total bonus across all employees is exactly k . After adding bonuses, each employee’s final salary becomes their original salary plus their assigned bonus. There are three structural...

CF 1297E - Modernization of Treeland

CF 1297E - Modernization of Treeland Rating: - Tags: *special, dfs and similar, trees Solve time: 3m 35s Verified: no Solution Problem Understanding We are given a tree of cities. From this tree we must choose a subset of cities $S$ such that two conditions hold simultaneously. First, if we only look at edges whose endpoints are both in $S$, the chosen vertices must remain connected, so $S$ forms a...

CF 1297C - Dream Team

CF 1297C - Dream Team Rating: - Tags: *special, greedy Solve time: 3m 24s Verified: no Solution Problem Understanding We are given an array of integers for each test case, where each value represents the contribution of a developer. We want to pick a subset of indices to form a team, and the value of the team is simply the sum of the chosen elements. If we had no restrictions,...

CF 1275A - Скрытый друг

CF 1275A - \u0421\u043a\u0440\u044b\u0442\u044b\u0439 \u0434\u0440\u0443\u0433 Rating: - Tags: *special Solve time: 4m 45s Verified: no Solution Problem Understanding We are given a directed friendship graph of $n$ users, where each user lists some other users as friends. The important detail is that friendship is not guaranteed to be mutual. If user $u$ lists $v$, it does not imply that $v$ lists $u$. The task is to detect all “hidden friendships”,...

VK Cup 2019 - Квалификация (Engine)

VK Cup 2019 - Квалификация (Engine) Special | 5 problems | 1/5 verified | Difficulty - | 15m 17s # Problem Rating Tags Accepted Time ✓ A \u0421\u043a\u0440\u044b\u0442\u044b\u0439 \u0434\u0440\u0443\u0433 *special 891 4m 45s B Code Review *special 844 2m 41s C #define \u0417\u0430\u0434\u0430\u0447\u0430 B ... *special 698 2m 4s ✓ E2 \u041a\u043e\u043d\u0442\u0440\u043e\u043b\u044c\u043d\u0430\u044f \u0441\u0443\u043c\u043c\u0430 *special 138 3m 19s F \u0428\u0430\u0440\u0434\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435 \u043f\u043e\u0441\u0442\u043e\u0432 *special, binary-search, interactive 92 2m 28s

CF 1275E2 - Контрольная сумма

CF 1275E2 - \u041a\u043e\u043d\u0442\u0440\u043e\u043b\u044c\u043d\u0430\u044f \u0441\u0443\u043c\u043c\u0430 Rating: - Tags: *special Solve time: 3m 19s Verified: no Solution Problem Understanding We are working with a byte array, and a checksum function, CRC32, that compresses the entire array into a single 32-bit value. The key property of CRC32 is linearity over the field GF(2), which means every byte contributes to the final checksum through a fixed linear transformation that depends on its position....

CF 1211G - King's Path

CF 1211G - King's Path Rating: 2500 Tags: *special, math, trees Solve time: 2m 51s Verified: yes Solution Problem Understanding We are given a tree where each node initially holds a color. There is also a target color for every node. The King performs a single walk on the tree. During this walk, whenever he traverses an edge, the endpoints of that edge swap their current flags. Because vertices can...

Microsoft Q# Coding Contest - Winter 2019

Microsoft Q# Coding Contest - Winter 2019 Special | 13 problems | 12/13 verified | Difficulty - | 11m 14s # Problem Rating Tags Accepted Time ✓ A1 [Generate state 00\u27e9 + 01\u27e9 + 10\u27e9]( https://codeforces.com/problemset/problem/1116/A1 ) A2 Generate equal superposition of four basis states *special 184 2m 38s ✓ B1 Distinguish three-qubit states *special 136 48s ✓ B2 Not A, not B or not C? *special 62 58s ✓...

CF 1116A2 - Generate equal superposition of four basis states

CF 1116A2 - Generate equal superposition of four basis states Rating: - Tags: *special Solve time: 2m 38s Verified: yes Solution Problem Understanding We start with a register of qubits initialized in the all-zero computational basis state. Alongside this, we are given four classical bitstrings of length $N$, each describing one computational basis state on these qubits. Each bitstring tells us which qubits should be flipped to obtain a specific...

CF 1057B - DDoS

CF 1057B - DDoS Rating: 1400 Tags: *special, brute force Solve time: 4m 25s Verified: yes Solution Problem Understanding We are given a timeline split into seconds. For each second, we know how many requests hit a server. This gives us an array where each position represents request volume in that second. We need to find the longest contiguous time interval such that the total number of requests inside that...

Mail.Ru Cup 2018 - Practice Round

Mail.Ru Cup 2018 - Practice Round Special | 3 problems | 2/3 verified | Difficulty 900-2000 | 12m 23s # Problem Rating Tags Accepted Time ✓ A Bmail Computer Network 900 *special, dfs-and-similar, trees 7,467 4m 52s ✓ B DDoS 1400 *special, brute-force 1,970 4m 25s ✓ C Tanya and Colored Candies 2000 *special, dp 1,171 3m 6s

CF 1057C - Tanya and Colored Candies

CF 1057C - Tanya and Colored Candies Rating: 2000 Tags: *special, dp Solve time: 3m 6s Verified: no Solution Problem Understanding We are given a row of candy boxes, each positioned at an integer coordinate. Every box contains a fixed number of candies, all sharing the same color, and each box is either red, green, or blue. We start at a specific box. From there, we can either walk left...

CF 1057A - Bmail Computer Network

CF 1057A - Bmail Computer Network Rating: 900 Tags: *special, dfs and similar, trees Solve time: 4m 52s Verified: yes Solution Problem Understanding We are given a growing network of routers that forms a tree rooted at router 1. Every router except the first was added one by one, and each new router was directly connected to exactly one earlier router. This means every router has a single parent, and...

VRt Contest 2019 (marathon)

VRt Contest 2019 (marathon) Special | 1 problems | 1/1 verified | Difficulty - | 2m 26s # Problem Rating Tags Accepted Time ✓ A2 Collaboration *special 2m 26s ✓

CF 1160A2 - Collaboration

CF 1160A2 - Collaboration Rating: - Tags: *special Solve time: 2m 26s Verified: yes Solution Problem Understanding We are given a base and a collection of job sites on a grid. Each job site describes a task located at a coordinate, with a fixed duration, a required number of workers, and a time window during which the job must finish. If we decide to execute a job, exactly that many...

Kotlin Heroes: Episode 7

Kotlin Heroes: Episode 7 Kotlin | 10 problems | 9/10 verified | Difficulty - | 43m 35s # Problem Rating Tags Accepted Time ✓ A Travel to Bertown *special, implementation, math 1,130 4m 13s ✓ B Nearest Point Function *special, implementation 816 4m 12s ✓ C Sweets *special, data-structures, implementation 484 4m 14s ✓ D String Searching *special, hashing 514 3m 31s ✓ E Chess Team Forming *special, binary-search, data-structures...

CF 1533I - Excursions

CF 1533I - Excursions Rating: - Tags: *special, constructive algorithms, dfs and similar, flows, graph matchings, graphs Solve time: 7m 26s Verified: yes Solution Problem Understanding We can view the situation as a two-layer directed routing process between two bipartite sets of nodes. One set corresponds to sights in Saratov, the other to sights in Engels. Each bus route is bidirectional in the sense that it can be used in...

CF 1533G - Biome Map

CF 1533G - Biome Map Rating: - Tags: *special, constructive algorithms, dfs and similar, graphs Solve time: 5m 39s Verified: no Solution Problem Understanding We are given a small grid of biome “types”, where each type is identified by a pair of parameters coming from a fixed $n \times m$ table. Some of these pairs exist and are assigned a unique integer identifier, while others are unavailable. Our task is...

CF 1533H - Submatrices

CF 1533H - Submatrices Rating: - Tags: *special, bitmasks, data structures, dp Solve time: 4m 23s Verified: yes Solution Problem Understanding We are working with a grid of uppercase letters, but the alphabet is extremely small: only the first five letters appear. The task is not to inspect individual cells, but to count how many rectangular subregions of this grid contain exactly a given number of distinct letters, from one...

CF 1533D - String Searching

CF 1533D - String Searching Rating: - Tags: *special, hashing Solve time: 3m 31s Verified: yes Solution Problem Understanding We are given a fixed collection of strings, all of the same length, and we are asked to answer many queries about a slightly longer string. Each stored string has length $m$. Each query string has length $m+1$. For a query string $t$, we want to count how many of the...

CF 1533C - Sweets

CF 1533C - Sweets Rating: - Tags: *special, data structures, implementation Solve time: 4m 14s Verified: yes Solution Problem Understanding We are given a circular arrangement of sweets labeled from 1 to n. Each sweet is either “liked” or “not liked”. Anya performs a deterministic process that removes sweets one by one from the circle. The process has two phases in every test case. First, if there is at least...

CF 1533A - Travel to Bertown

CF 1533A - Travel to Bertown Rating: - Tags: *special, implementation, math Solve time: 4m 13s Verified: yes Solution Problem Understanding Vika arrives in Bertown on a fixed day $k$. She has several friends, and each friend offers a single continuous interval of days during which she can stay at their home. The constraint is that she can choose at most one friend, and once she chooses, she can only...

CF 1533B - Nearest Point Function

CF 1533B - Nearest Point Function Rating: - Tags: *special, implementation Solve time: 4m 12s Verified: yes Solution Problem Understanding We are given several test cases, each consisting of a sorted array of distinct integers. Think of these numbers as fixed points on a number line. A query point $y$ is chosen, and a function returns the closest point in the array to $y$ based on absolute distance. The function...

CF 1532F - Prefixes and Suffixes

CF 1532F - Prefixes and Suffixes Rating: - Tags: *special, strings Solve time: 4m 24s Verified: no Solution Problem Understanding We are given a multiset of strings that all come from a single unknown string of length $n$. For every length $k$ from $1$ to $n-1$, we are given exactly two strings of that length, and each of those two strings is either a prefix or a suffix of the...

Kotlin Heroes: Practice 7

Kotlin Heroes: Practice 7 Kotlin | 6 problems | 3/6 verified | Difficulty - | 19m 14s # Problem Rating Tags Accepted Time ✓ A A+B (Trial Problem) *special 1,150 2m 54s ✓ B Frog Jumping *special, math 829 2m 47s ✓ C Uniform String *special, implementation 641 4m 20s D Teams Forming *special, sortings 590 1m 21s ✓ E Good Array *special 392 3m 28s F Prefixes and Suffixes...

CF 1532E - Good Array

CF 1532E - Good Array Rating: - Tags: *special Solve time: 3m 28s Verified: no Solution Problem Understanding We are given an array of integers and we are allowed to remove exactly one element at a time. For each removal, we look at the remaining array and ask a very specific question: does there exist an element that is exactly equal to the sum of all the other elements in...

CF 1532C - Uniform String

CF 1532C - Uniform String Rating: - Tags: *special, implementation Solve time: 4m 20s Verified: no Solution Problem Understanding We are building strings under a very specific constraint: each string must use only the first k lowercase Latin letters, and each of those k letters must appear at least once. Among all such valid strings of length n, we want to make the least frequent character as large as possible....

CF 1532A - A+B (Trial Problem)

CF 1532A - A+B (Trial Problem) Rating: - Tags: *special Solve time: 2m 54s Verified: yes Solution Problem Understanding We are given a sequence of independent queries. Each query consists of two integers, and for every pair we must compute their arithmetic sum and output it immediately. There is no dependency between test cases. Each pair can be processed in isolation, so the problem reduces to repeatedly applying a single...

CF 1532B - Frog Jumping

CF 1532B - Frog Jumping Rating: - Tags: *special, math Solve time: 2m 47s Verified: yes Solution Problem Understanding The frog moves along a straight number line starting from position 0. Its motion is fully deterministic: it alternates between two fixed step sizes. On the first move it goes right by distance a , on the second move it goes left by b , then right by a again, then...

CF 1356A4 - Distinguish I ⊗ X from CNOT Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 4m 1s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e35a3-b71c-83ec-9e42-9d4fb90e2a55 Solution Problem Understanding We are given a black-box quantum operation that acts on exactly two qubits. Internally, it is guaranteed to be one of two possibilities. Either it behaves like a bit flip applied only to the second qubit while leaving the first unchanged, or...

CF 1331F - Elementary! Rating: ? Tags: *special, brute force, dp, strings Model: gpt-5-3-mini Solve time: 3m 35s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e0520-15e8-83ec-9154-9ddf48731367 Solution Problem Understanding We are given a single string consisting only of uppercase English letters, with length at most 10. The task is to decide whether this string satisfies a hidden structural property and output either YES or NO. Because the string is extremely short, the...

CF 1356A1 - Distinguish I from X Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 4m Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e359e-2710-83ec-9b90-d0d8ed8032f9 Solution Problem Understanding We are given a black-box single-qubit quantum operation. The operation is guaranteed to be exactly one of two possibilities: either it does nothing to the qubit (the identity transformation), or it flips the computational basis state (the X gate, which maps a zero state to...

CF 1357D5 - Quantum Classification - Dataset 7 Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 2m 50s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e37c0-40b4-83ec-9672-180110b3f6ac Solution Problem Understanding We are dealing with a classification system where inputs are interpreted as objects with hidden structure, and the task is to assign each object to a category according to a fixed rule defined by the problem’s model. The key idea is that each...

CF 1357B2 - "Is the number divisible by 3?" oracle Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 1m 50s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e370b-19f0-83ec-952c-50939dee7804 Solution Problem Understanding The task is to implement a reversible quantum oracle that marks bit strings representing numbers divisible by 3. The input is a register of up to 8 qubits, which encodes a binary integer in little-endian order, plus one extra qubit that...

CF 1356D2 - Quantum Classification - 2 Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 1m 56s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e361c-7878-83ec-81a6-39db5a72ceec Solution Problem Understanding We are given a fixed dataset of 200 points in a two-dimensional space. Each point has two real-valued features, both in the range $[-1, 1]$, and each point is labeled as either class 0 or class 1. The task is not to compute anything...

CF 1357D4 - Quantum Classification - Dataset 6 Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 2m 39s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e37af-4440-83ec-b9d9-ebe7597fba26 Solution Problem Understanding We are given a training dataset consisting of labeled examples, where each example has a feature representation and an associated class. After processing this dataset, we must answer classification queries for unseen feature points, assigning each query point to one of the learned...

CF 1346F - Dune II: Battle For Arrakis Rating: 2000 Tags: *special, data structures, greedy, math Model: gpt-5-3-mini Solve time: 4m 17s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e23f6-cbe8-83ec-b3d6-17ce363f4940 Solution Problem Understanding The grid represents a battlefield where each cell contains some number of identical units. The goal is to choose one destination cell and move every unit from every other cell into it. A single move shifts exactly one unit...

CF 1275E3 - Контрольная сумма Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 3m 1s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a2d9641-a084-83ec-82e8-deb7a3bc6120 Solution Problem Understanding We are given a byte array that represents a file and a checksum function, CRC32, that maps the entire array into a 32-bit value. A query modifies the array in a very specific way: four consecutive bytes at position i are overwritten with fixed values x0..x3...

CF 1275D - Storage2 Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 2m 45s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2d958a-5f24-83ec-85cc-77f5bcde4b18 Solution Problem Understanding We are given a fixed storage system consisting of 28 blocks arranged conceptually as a 4 by 7 grid. The first 15 blocks are original image pieces, and the remaining 13 are redundancy codes constructed in such a way that they allow recovery of missing data through...

CF 1275E1 - Контрольная сумма Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 3m 38s Verified: no (0/1 samples) Share: https://chatgpt.com/share/6a2d9646-f420-83ec-ac50-8e8bd7e5341d Solution Problem Understanding We are given a byte array and a hash function applied to it: CRC32. For every query, we imagine performing a modification in two separate places of the array. In the first segment of four consecutive bytes, we are forced to overwrite them with a fixed...

CF 1331C - ...And after happily lived ever they Rating: ? Tags: *special, bitmasks Model: gpt-5-5 Solve time: 5m 18s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e0474-2e44-83ec-841e-f2d641d79b62 Solution Problem Understanding The task is extremely minimal on the surface: we are given a single integer a , guaranteed to lie in the range from 0 to 63, and we must output exactly one integer. The constraint immediately suggests that the input is...

CF 1357A4 - Distinguish Rz from R1 Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 1m 31s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e36a3-7998-83ec-bb79-e926239f63a4 Solution Problem Understanding We are given a black-box single-qubit operation that is guaranteed to be one of two possible quantum rotations. Both act on a single qubit and accept an angle parameter, but they differ in how that angle is embedded into the quantum state. Our task...

CF 1356B1 - Increment Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 4m 1s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e35a2-01ec-83ec-8835-a5ff33088f62 Solution Problem Understanding We are asked to implement a reversible quantum operation that increments an N-bit binary number stored in a register. The register is given in little-endian format, meaning the first qubit represents the least significant bit and the last qubit represents the most significant bit. The operation must...

CF 1357C1 - Prepare superposition of basis states with 0s Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 1m 53s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e3711-089c-83ec-9f78-ece22aab110d Solution Problem Understanding We start with an N-qubit system initially in the all-zero computational basis state. The goal is to transform this state into a uniform quantum superposition over a restricted subset of basis states: all bitstrings of length N that contain at least...

CF 1356C - Prepare state |01⟩ + |10⟩ + |11⟩ Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 2m 19s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e3624-797c-83ec-8080-abe6b68837ae Solution Problem Understanding We start from two qubits fixed in the basis state |00⟩ and must transform them into a specific entangled superposition. The target state assigns zero probability to |00⟩ and spreads equal amplitude across the remaining three basis states |01⟩, |10⟩, and...

CF 1357D1 - Quantum Classification - Dataset 3 Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 1m 42s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e3710-1fe8-83ec-a940-a1b73b4d39ca Solution Problem Understanding The task is not a typical algorithmic problem with explicit inputs and outputs during execution. Instead, we are given a fixed dataset of 400 two-dimensional points, each labeled as either class 0 or class 1, and we must produce a trained quantum classifier...

CF 1357D2 - Quantum Classification - Dataset 4 Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 2m Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e3785-2640-83ec-b680-5030521a03fc Solution Problem Understanding We are given a hidden structure over a set of items, where each item belongs to one of two classes, but we are not allowed to observe the labels directly. Instead, the only way to obtain information is through an oracle that responds to...

CF 1357A3 - Distinguish H from X Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 1m 42s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e36b4-8588-83ec-99a8-206f55c8a287 Solution Problem Understanding We are given a black-box single-qubit quantum operation that is guaranteed to be exactly one of two possibilities: the Hadamard gate or the Pauli-X gate. Our task is not to simulate it, but to identify which one it is using a small number of...

CF 1346H - Game with Segments Rating: 2700 Tags: *special, data structures, games Model: gpt-5-3-mini Solve time: 2m 21s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e23b1-4140-83ec-9c31-41f2c214dfd1 Solution Problem Understanding We are given an interval on a number line as a starting position, and a collection of special target intervals called terminal segments. A move consists of shrinking the current interval by exactly one unit from either the left side or the...

CF 1357A7 - Distinguish Y, XZ, -Y and -XZ Rating: ? Tags: *special Model: gpt-5-3-mini Solve time: 1m 25s Verified: yes (0/0 samples) Share: https://chatgpt.com/share/6a2e369e-ab7c-83ec-b652-ef7a3c497fa6 Solution Problem Understanding We are given access to a black-box single-qubit quantum operation. Internally, it is guaranteed to be one of four possibilities: either a Pauli Y gate (possibly multiplied by a global phase of −1), or the composition of Z followed by X (again...

CF 1331E - Jordan Smiley Rating: ? Tags: *special, dfs and similar, geometry, implementation Model: gpt-5-3-mini Solve time: 4m 30s Verified: yes (1/1 samples) Share: https://chatgpt.com/share/6a2e0448-ddd8-83ec-a640-42ed2a7f9fae Solution Problem Understanding The input describes a point on an infinite grid, identified by two non-negative integers, row and col . This grid is not interpreted as a standard Cartesian plane where every cell is equivalent. Instead, it is part of a geometric construction...

CF 1211I - Unusual Graph

CF 1211I - Unusual Graph Rating: 3000 Tags: *special, graphs Solve time: 2m 22s Verified: yes Solution Problem Understanding We are given an undirected graph with up to 500 vertices. The graph is known to come from a very specific hidden labeling process: each vertex originally had a number between 0 and 15, and an edge existed between two vertices if and only if their labels differ in exactly one...

CF 1211D - Teams

CF 1211D - Teams Rating: 2000 Tags: *special, binary search, greedy, math Solve time: 6m 33s Verified: yes Solution Problem Understanding We are given a multiset of player ratings. Each player can be used at most once, and our goal is to form as many disjoint teams as possible under a strict structure constraint. Every valid team consists of two homogeneous groups of players. One group has exactly a players,...

CEOI 2019 day 2 online mirror (unrated, IOI format)

CEOI 2019 day 2 online mirror (unrated, IOI format) Type: ICPC/IOI | Problems: 3 | Verified: 1/3 | Rating range: - | Time: 15m 20s Problem Name Rating Tags Solve Time Verified A Amusement Park - *special, dp, math 4m 1s ✓ B Magic Tree - *special, data-structures, dp 3m 55s ✗ C Scissors and Tape - *special, constructive-algorithms, geometry 7m 24s ✗

CF 1193C - Scissors and Tape

CF 1193C - Scissors and Tape Rating: - Tags: *special, constructive algorithms, geometry Solve time: 7m 24s Verified: no Solution Problem Understanding We are given two simple polygons in the plane, an initial shape and a target shape. Both polygons have equal area, but their geometry can be completely different. The task is not to compute a direct geometric transformation, but to describe a sequence of allowed “manufacturing steps” that...

CF 1193A - Amusement Park

CF 1193A - Amusement Park Rating: - Tags: *special, dp, math Solve time: 4m 1s Verified: yes Solution Problem Understanding We are given a set of attractions and some planned one-way slides between pairs of them. After construction, each slide can be reversed or kept as is, independently of others. What we ultimately choose is therefore just a direction for every existing edge. A proposal is considered physically valid if...

CF 1193B - Magic Tree

CF 1193B - Magic Tree Rating: - Tags: *special, data structures, dp, trees Solve time: 3m 55s Verified: no Solution Problem Understanding We are given a rooted tree where vertex 1 is the root, and each other vertex has exactly one parent, so the structure is fixed and acyclic. Some non-root vertices contain a single fruit. Each fruit has a specific vertex, a day on which it becomes ripe, and...

CF 1192C - Cubeword

CF 1192C - Cubeword Rating: - Tags: *special, brute force, dp, meet-in-the-middle Solve time: 7m 17s Verified: yes Solution Problem Understanding We are given a collection of strings that can be placed on the edges of a cube. Each string has length between 3 and 10, and we are allowed to use any of them repeatedly. A valid construction consists of taking a cube and assigning one string to each...

CF 1192B - Dynamic Diameter

CF 1192B - Dynamic Diameter Rating: - Tags: *special, data structures, dfs and similar, divide and conquer, trees Solve time: 3m 58s Verified: no Solution

CEOI 2019 day 1 online mirror (unrated, IOI format)

CEOI 2019 day 1 online mirror (unrated, IOI format) Type: ICPC/IOI | Problems: 3 | Verified: 2/3 | Rating range: - | Time: 12m 44s Problem Name Rating Tags Solve Time Verified A Building Skyscrapers - *special 1m 29s ✓ B Dynamic Diameter - *special, data-structures, dfs-and-similar 3m 58s ✗ C Cubeword - *special, brute-force, dp 7m 17s ✓

CF 1115U1 - Anti-diagonal unitary

CF 1115U1 - Anti-diagonal unitary Rating: 1500 Tags: *special Solve time: 1m 6s Verified: yes Solution Problem Understanding We are asked to implement a quantum operation on an array of qubits. The operation must correspond to a unitary matrix whose only non-zero entries lie on the anti-diagonal. For a system of $N$ qubits, the state space has dimension $2^N$. The matrix describing the operation is therefore a $2^N \times 2^N$...

Microsoft Q# Coding Contest - Winter 2019 - Warmup

Microsoft Q# Coding Contest - Winter 2019 - Warmup Type: Special | Problems: 6 | Verified: 6/6 | Rating range: 1100-1700 | Time: 5m 11s Problem Name Rating Tags Solve Time Verified G1 AND oracle 1100 *special 43s ✓ G2 OR oracle 1600 *special 54s ✓ G3 Palindrome checker oracle 1600 *special 52s ✓ U1 Anti-diagonal unitary 1500 *special 1m 6s ✓ U2 Chessboard unitary 1600 *special 46s ✓ U3...

CF 1115U3 - Block unitary

CF 1115U3 - Block unitary Rating: 1700 Tags: *special Solve time: 50s Verified: yes Solution Problem Understanding We are asked to implement a quantum unitary operation on $N$ qubits, where $N$ is small, between 2 and 5. The operation is represented by a $2^N \times 2^N$ matrix with a specific block structure. The matrix can be visualized as four quarters: Top-left quarter: an anti-diagonal matrix of size $2^{N-1}$, meaning ones...

CF 1115U2 - Chessboard unitary

CF 1115U2 - Chessboard unitary Rating: 1600 Tags: *special Solve time: 46s Verified: yes Solution Problem Understanding We are asked to implement a unitary operation on $N$ qubits, where $2 \le N \le 5$. The operation is represented by a $2^N \times 2^N$ matrix with a chessboard-like pattern of zeros and non-zero elements. Specifically, 2x2 blocks alternate between non-zero and zero values, with the top-left 2x2 block being non-zero. The...

CF 1115G2 - OR oracle

CF 1115G2 - OR oracle Rating: 1600 Tags: *special Solve time: 54s Verified: yes Solution Problem Understanding We are given a small quantum register of at most eight qubits that encode an input bitstring $x_0, x_1, \dots, x_{N-1}$, along with one extra qubit $y$ that acts as an output wire. The task is to implement a reversible transformation that computes whether at least one of the input bits is equal...

CF 1115G3 - Palindrome checker oracle

CF 1115G3 - Palindrome checker oracle Rating: 1600 Tags: *special Solve time: 52s Verified: yes Solution Problem Understanding We are asked to implement a quantum oracle acting on a small register of qubits. The oracle receives an input string encoded in quantum form, represented by an array of up to eight qubits, plus one additional qubit that serves as the output bit. The required transformation is the standard reversible oracle...

CF 1115G1 - AND oracle

CF 1115G1 - AND oracle Rating: 1100 Tags: *special Solve time: 43s Verified: yes Solution Problem Understanding We are asked to implement a quantum operation that computes the logical AND of an array of qubits. Concretely, we have a set of $N$ qubits, each representing a binary value (0 or 1, though they can be in superposition), and a single output qubit. The task is to apply a transformation such...

CF 1116D6 - Hessenberg matrix

CF 1116D6 - Hessenberg matrix Rating: - Tags: *special Solve time: 43s Verified: yes Solution Problem Understanding We are asked to implement a quantum operation on a small number of qubits (2 to 4) such that the unitary matrix representing it has an upper Hessenberg form. Concretely, for a matrix of size $2^N \times 2^N$, all entries below the first subdiagonal must be zero, while the first subdiagonal and all...

CF 1116D5 - Creeper

CF 1116D5 - Creeper Rating: - Tags: *special Solve time: 51s Verified: yes Solution Problem Understanding We are given a very specific 8×8 pattern describing where a 3-qubit unitary matrix has non-negligible entries. The matrix is not arbitrary, it is extremely sparse and structured, and the task is to implement any quantum circuit on 3 qubits whose unitary matches this sparsity pattern. Each matrix entry corresponds to a transition between...

CF 1116D4 - TIE fighter

CF 1116D4 - TIE fighter Rating: - Tags: *special Solve time: 41s Verified: yes Solution Problem Understanding We are asked to implement a quantum operation on an array of $N$ qubits, where $N$ ranges from 2 to 5. The core requirement is that the operation's unitary matrix has a very particular pattern: a central 2x2 submatrix filled with non-zero values, anti-diagonals in the top-left and bottom-right corners, and diagonals in...

CF 1116D3 - X-wing fighter

CF 1116D3 - X-wing fighter Rating: - Tags: *special Solve time: 56s Verified: yes Solution Problem Understanding We are asked to implement a unitary operation on a quantum register consisting of $N$ qubits, where $2 \le N \le 5$. The unitary is represented as a $2^N \times 2^N$ matrix, and it must have non-zero entries only on the main diagonal and the anti-diagonal. All other entries must be zero. The...

CF 1116D2 - Pattern of increasing blocks

CF 1116D2 - Pattern of increasing blocks Rating: - Tags: *special Solve time: 47s Verified: yes Solution Problem Understanding We are asked to construct a quantum operation on $N$ qubits whose matrix, in the computational basis, has a very rigid block structure. The full unitary is a $2^N \times 2^N$ matrix, and we are not required to compute or print it explicitly. Instead, we must design a quantum circuit whose...

CF 1116D1 - Block diagonal matrix

CF 1116D1 - Block diagonal matrix Rating: - Tags: *special Solve time: 43s Verified: yes Solution Problem Understanding We are asked to implement a unitary operation on an array of $N$ qubits, where $2 \le N \le 5$, such that the matrix representing the operation has a very specific block-diagonal structure. In concrete terms, for $2^N \times 2^N$ matrices, all non-zero entries appear in consecutive 2×2 blocks along the main...

CF 1116C3 - ``Is the number of ones divisible by 3?'' oracle

CF 1116C3 - ``Is the number of ones divisible by 3?'' oracle Rating: - Tags: *special Solve time: 48s Verified: yes Solution Problem Understanding We are given a small register of qubits that encode a bitstring and an additional single qubit that acts as an output accumulator. The task is to implement a reversible transformation that computes a Boolean function on the bitstring: we need to flip the output qubit...

CF 1116C2 - ``Is the bit string periodic?'' oracle

CF 1116C2 - ``Is the bit string periodic?'' oracle Rating: - Tags: *special Solve time: 41s Verified: yes Solution Problem Understanding We are asked to implement a quantum oracle that checks whether a given bit string is periodic. In practical terms, imagine we have an array of $N$ qubits, each representing a bit, and a separate output qubit. The goal is to flip the output qubit if and only if...

CF 1116B2 - Not A, not B or not C?

CF 1116B2 - Not A, not B or not C? Rating: - Tags: *special Solve time: 58s Verified: yes Solution Problem Understanding We are asked to work with a single qubit that is guaranteed to be in one of three specific quantum states: $|A\rangle$, $|B\rangle$, or $|C\rangle$. Each of these states is a superposition of $|0\rangle$ and $|1\rangle$ with complex coefficients: $|A\rangle$ uses $1$ and $1$, $|B\rangle$ uses $1$ and...

CF 1116C1 - Alternating bits oracle

CF 1116C1 - Alternating bits oracle Rating: - Tags: *special Solve time: 40s Verified: yes Solution Problem Understanding We are asked to implement a "quantum oracle" that checks whether a binary vector alternates. That means for an input array of bits x[0..N-1] , we need to determine if no two consecutive bits are the same. Formally, the function $f(x)$ outputs 1 if every adjacent pair (x[i], x[i+1]) satisfies x[i] !=...

CF 1116B1 - Distinguish three-qubit states

CF 1116B1 - Distinguish three-qubit states Rating: - Tags: *special Solve time: 48s Verified: yes Solution Problem Understanding We are given three qubits in one of two specific entangled states, each a superposition of three computational basis states with complex coefficients derived from the cube roots of unity. The two states differ only in the phase factors applied to the second and third qubits. The task is to implement a...

April Fools Day Contest 2019

April Fools Day Contest 2019 Type: April Fools | Problems: 7 | Verified: 7/7 | Rating range: - | Time: 11m 54s Problem Name Rating Tags Solve Time Verified A Thanos Sort - *special, implementation 1m 23s ✓ B Kanban Numbers - *special, brute-force 1m 36s ✓ C Mystery Circuit - bitmasks, brute-force 1m 52s ✓ D Pigeon d'Or - *special, implementation 1m 39s ✓ E Fourier Doodles - -...

CF 1145F - Neat Words

CF 1145F - Neat Words Rating: - Tags: *special Solve time: 3m 11s Verified: yes Solution Problem Understanding We are given a single string of uppercase letters with length between 1 and 10. The task is to determine whether this string is "neat." A neat word, in this context, is defined as one where no letter appears more than once at even positions or more than once at odd positions....

CF 1145G - AI Takeover

CF 1145G - AI Takeover Rating: - Tags: *special, interactive Solve time: 59s Verified: yes Solution Problem Understanding This is an interactive game against a fixed but unknown opponent program. The opponent chooses one deterministic strategy at the beginning of the test and sticks to it for all 20 rounds. Your task is to play rock-paper-scissors and interactively discover enough about that strategy to guarantee a win streak of at...

CF 1145D - Pigeon d'Or

CF 1145D - Pigeon d'Or Rating: - Tags: *special, implementation Solve time: 1m 39s Verified: yes Solution Problem Understanding We are given a small array of integers, each between 1 and 32, and we are asked to find a certain integer that represents the maximum number of consecutive elements that satisfy a bitwise property. Specifically, the problem asks us to find the largest subset of elements where the bitwise AND...

CF 1145B - Kanban Numbers

CF 1145B - Kanban Numbers Rating: - Tags: *special, brute force Solve time: 1m 36s Verified: yes Solution Problem Understanding We are asked to determine whether a given number can be represented as the sum of any number of integers equal to 4 or 7. The input is a single integer $a$ between 1 and 99, and the output is either "YES" if such a representation exists, or "NO" otherwise....

CF 1145A - Thanos Sort

CF 1145A - Thanos Sort Rating: - Tags: *special, implementation Solve time: 1m 23s Verified: yes Solution Problem Understanding We start with an array whose length is a power of two. The allowed operation is very unusual: whenever the current array is not sorted in non-decreasing order, we may delete either its left half or its right half. After that, we repeat the same process on the remaining half. Because...

CF 1170I - Good Subsets

CF 1170I - Good Subsets Rating: - Tags: *special, dp Solve time: 1m 56s Verified: yes Solution Problem Understanding We are given a set of segments on the real line, each defined by its left and right endpoints. The task is to count subsets of these segments whose union exactly equals the union of all segments. In other words, we want the number of ways to pick segments such that...

CF 1170B - Bad Days

CF 1170B - Bad Days Rating: - Tags: *special, implementation Solve time: 3m 12s Verified: yes Solution Problem Understanding We are given a sequence of daily website visit counts. Each position represents one day, and the value at that position represents how many visits occurred on that day. We need to examine every day and decide whether it is “bad”. A day becomes bad if, when looking only at the...

CF 1192A - Building Skyscrapers

CF 1192A - Building Skyscrapers Rating: - Tags: *special Solve time: 1m 29s Verified: yes Solution Problem Understanding We are given a set of points on an infinite grid. Each point represents a building site that must eventually be occupied by a skyscraper. We must decide an order to construct these skyscrapers one by one. Two constraints govern whether a building step is valid. First, every new building after the...

CF 1211F - kotlinkotlinkotlinkotlin...

CF 1211F - kotlinkotlinkotlinkotlin... Rating: 2300 Tags: *special, graphs, implementation, strings Solve time: 1m 48s Verified: yes Solution Problem Understanding We are given a collection of string fragments. Originally, all of them came from cutting a long string that consisted of the word "kotlin" repeated several times. After the cuts, the fragments were shuffled. Our task is to recover any ordering of the fragments such that their concatenation becomes kotlin...

CF 1211B - Traveling Around the Golden Ring of Berland

CF 1211B - Traveling Around the Golden Ring of Berland Rating: 1500 Tags: *special, implementation Solve time: 1m 38s Verified: yes Solution Problem Understanding We are asked to plan the minimum number of visits for a tourist traveling along a fixed cyclic route of cities. The cities are numbered from 1 to n, arranged in a cycle, and the traveler always moves forward: from city i to i+1, and from...

CF 1275F - Шардирование постов

CF 1275F - \u0428\u0430\u0440\u0434\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435 \u043f\u043e\u0441\u0442\u043e\u0432 Rating: - Tags: *special, binary search, interactive Solve time: 2m 28s Verified: no Solution There is not enough information to diagnose the bug or provide a corrected solution. The sample 3 3 tab one bat with expected output 6 tabbat appears to belong to a string construction problem, but you have not provided: the problem statement, the original Python solution, or even the name of...

CF 1275B - Code Review

CF 1275B - Code Review Rating: - Tags: *special Solve time: 2m 41s Verified: no Solution There is not enough information to diagnose the bug or provide a corrected solution. The sample 3 3 tab one bat with expected output 6 tabbat appears to belong to a string construction problem, but you have not provided: the problem statement, the original Python solution, or even the name of the problem. Without...

CF 1275C - #define Задача B ...

CF 1275C - #define \u0417\u0430\u0434\u0430\u0447\u0430 B ... Rating: - Tags: *special Solve time: 2m 4s Verified: yes Solution Problem Understanding We are asked to simulate a massive array defined recursively using C-style macros. The macros expand in a very structured way: each macro level quadruples the number of elements generated by the previous level, with simple offsets added. At the base level, A0(x) produces a single value x . Then...

CF 1297B - Cartoons

CF 1297B - Cartoons Rating: - Tags: *special, implementation, sortings Solve time: 3m 5s Verified: no Solution There is not enough information to diagnose the bug or provide a corrected solution. The sample 3 3 tab one bat with expected output 6 tabbat appears to belong to a string construction problem, but you have not provided: the problem statement, the original Python solution, or even the name of the problem....

CF 1297A - Likes Display

CF 1297A - Likes Display Rating: - Tags: *special, implementation Solve time: 1m 57s Verified: yes Solution Problem Understanding The task is to convert a raw number of likes into a compact, human-readable format for display. Numbers less than a thousand remain as-is, numbers in the thousands are rounded to the nearest thousand with a 'K' suffix, and numbers in the millions are rounded to the nearest million with an...

Kotlin Heroes: Episode 4

Kotlin Heroes: Episode 4 Kotlin | 9 problems | 4/9 verified | Difficulty 1000-2900 | 40m 15s # Problem Rating Tags Accepted Time ✓ A Color Revolution 1000 *special, math 2,202 11m 53s ✓ B Boot Camp 1400 *special, greedy 1,252 3m 10s C Spring Cleaning 1600 *special, greedy, sortings 677 5m 16s D Constructing the Dungeon 1600 *special, graphs, greedy 544 2m 56s ✓ E Magic Tricks 1700 *special,...

CF 1331H - It's showtime

CF 1331H - It's showtime Rating: - Tags: *special Solve time: 3m 27s Verified: no Solution Problem Understanding The problem presents a single integer input that encodes two pieces of information. The integer can be decomposed as input = 1000 * n + mod , where n is the number for which we want the double factorial and mod is the modulus to compute it under. Our task is to...

CF 1331B - Limericks

CF 1331B - Limericks Rating: - Tags: *special, math, number theory Solve time: 3m 36s Verified: no Solution Problem Understanding The problem asks us to compute a specific numeric property related to an integer input, denoted as a . While the problem statement is written in a poetic form, the underlying task is to find the number of integers less than a that are coprime to a . In other...

CF 1331A - Is it rated?

CF 1331A - Is it rated? Rating: - Tags: *special Solve time: 3m 12s Verified: no Solution Correctness The solution does not successfully establish what Exercise 4.6.3.13 asks. The positive part is that the displayed constructions are now genuine star chains. In each case the chain first builds $$1,2,4,\ldots,2^m,$$ and then appends terms by adding previously occurring powers of two. Every displayed step is indeed of the form $$a_r=a_{r-1}+a_j,$$ with...

CF 1346A - Color Revolution

CF 1346A - Color Revolution Rating: 1000 Tags: *special, math Solve time: 11m 53s Verified: yes Solution Problem Understanding We are given a total number of participants and a fixed multiplier. The participants must be split into four consecutive groups where each next group is exactly $k$ times larger than the previous one. Once the first group size is fixed, the rest is completely determined as a geometric progression: $$n_1,;...

CF 1346G - Two IP Cameras

CF 1346G - Two IP Cameras Rating: 2300 Tags: *special, math, number theory Solve time: 1m 20s Verified: no Solution Problem Understanding We are given two identical IP cameras, each capable of taking photos at a fixed period. The period of each camera must be chosen from a predefined set of integers, but the starting moment of each camera is flexible. The goal is to cover a set of moments...

CF 1346B - Boot Camp

CF 1346B - Boot Camp Rating: 1400 Tags: *special, greedy Solve time: 3m 10s Verified: no Solution Problem Understanding The problem asks us to schedule the maximum number of lectures during a programming boot camp that lasts n days. Each day is either a normal day, where we can hold lectures, or an excursion day, where no lectures are allowed. On normal days, we cannot schedule more than k_1 lectures...

CF 1356B2 - Decrement

CF 1356B2 - Decrement Rating: - Tags: *special Solve time: 2m 48s Verified: no Solution Solution We work modulo an odd prime $p$ and factor $$x^8 + 1.$$ The structure of the factorization depends entirely on how $-1$ and $2$ behave in $\mathbb{F}_p$, because the natural attempt is to rewrite $x^8+1$ as a product of quadratic expressions obtained from square roots of these elements. We begin from the identity $$x^8...

Microsoft Q# Coding Contest - Summer 2020 - Warmup

Microsoft Q# Coding Contest - Summer 2020 - Warmup Type: Special | Problems: 5 | Verified: 4/5 | Rating range: - | Time: 8m 51s Problem Name Rating Tags Solve Time Verified A2 Distinguish I from Z - *special 2m 1s ✓ A3 Distinguish Z from S - *special 1m 30s ✓ A5 Distinguish Z from -Z - *special 1m 25s ✓ B2 Decrement - *special 2m 48s ✗ D1...

CF 1356D1 - Quantum Classification - 1

CF 1356D1 - Quantum Classification - 1 Rating: - Tags: *special Solve time: 1m 7s Verified: yes Solution Problem Understanding The task is not a typical input-output problem. Instead, you are given a fixed dataset of 200 two-dimensional points, each labeled as either class 0 or class 1. The real goal is to design a quantum-inspired classifier by choosing a circuit structure and a small set of parameters, then outputting...

CF 1356A5 - Distinguish Z from -Z

CF 1356A5 - Distinguish Z from -Z Rating: - Tags: *special Solve time: 1m 25s Verified: yes Solution Problem Understanding We are given a quantum operation acting on a single qubit. The operation is either a Z gate, which leaves the |1⟩ component of a qubit unchanged and flips the phase of |0⟩, or a -Z gate, which flips the phase of |0⟩ and adds an extra negative sign globally...

CF 1356A2 - Distinguish I from Z

CF 1356A2 - Distinguish I from Z Rating: - Tags: *special Solve time: 2m 1s Verified: yes Solution Problem Understanding We are given a quantum black-box operation that acts on a single qubit. The operation is guaranteed to be either doing nothing at all or applying a phase flip. We need to identify which of these two behaviors is implemented and output a binary label. The difficulty is that the...

CF 1356A3 - Distinguish Z from S

CF 1356A3 - Distinguish Z from S Rating: - Tags: *special Solve time: 1m 30s Verified: yes Solution Problem Understanding We are given a quantum black-box operation that acts on a single qubit. This operation is guaranteed to be either the Z gate or the S gate. Both gates have well-defined mathematical actions on qubit states: Z multiplies the |1⟩ component by −1, leaving |0⟩ unchanged, while S multiplies |1⟩...

CF 1357E2 - Root of quantum Fourier transform

CF 1357E2 - Root of quantum Fourier transform Rating: - Tags: *special Solve time: 1m 46s Verified: yes Solution Problem Understanding The task is to implement a quantum operation that, when applied $P$ times, reproduces the effect of a full quantum Fourier transform (QFT) on a small register of qubits. The input is an integer $P$ between 2 and 8 and a quantum register in little-endian format, where each qubit...

Microsoft Q# Coding Contest - Summer 2020

Microsoft Q# Coding Contest - Summer 2020 Type: Special | Problems: 9 | Verified: 9/9 | Rating range: - | Time: 20m 17s Problem Name Rating Tags Solve Time Verified A1 Figure out direction of CNOT - *special 1m 51s ✓ A2 Distinguish I, CNOTs and SWAP - *special 1m 40s ✓ A5 Distinguish Rz(\u03b8) from Ry(\u03b8) - *special 1m 38s ✓ A6 Distinguish four Pauli gates - *special 6m...

CF 1357E1 - Power of quantum Fourier transform

CF 1357E1 - Power of quantum Fourier transform Rating: - Tags: *special Solve time: 2m 2s Verified: yes Solution Problem Understanding The task is to implement an operation on a quantum register that corresponds to raising the quantum Fourier transform (QFT) to a given power $P$. The input is an integer $P$ and a quantum register encoded in little-endian format, meaning the least significant qubit comes first. The output is...

CF 1357D3 - Quantum Classification - Dataset 5

CF 1357D3 - Quantum Classification - Dataset 5 Rating: - Tags: *special Solve time: 1m 38s Verified: yes Solution Problem Understanding In this problem, we are given an array of integers representing a dataset of measurements. Each query requires us to compute the minimum number of operations needed to make a segment of this array “homogeneous” according to a specific rule: all identical numbers in a contiguous subsequence should be...

CF 1357A6 - Distinguish four Pauli gates

CF 1357A6 - Distinguish four Pauli gates Rating: - Tags: *special Solve time: 6m 15s Verified: yes Solution Problem Understanding We are given a black-box quantum operation that acts on a single qubit. This operation is guaranteed to be exactly one of four possibilities: the identity operation or one of the three Pauli gates. Our task is to identify which of the four it is and return an integer label...

CF 1357C2 - Prepare superposition of basis states with the same parity

CF 1357C2 - Prepare superposition of basis states with the same parity Rating: - Tags: *special Solve time: 1m 45s Verified: yes Solution Problem Understanding The problem asks us to prepare a quantum state over $N$ qubits where only the basis states with a specific parity of ones are included in an equal superposition. Here, parity 0 means we include all bitstrings with an even number of ones, and parity...

CF 1357B1 - "Is the bit string balanced?" oracle

CF 1357B1 - "Is the bit string balanced?" oracle Rating: - Tags: *special Solve time: 1m 42s Verified: yes Solution Problem Understanding We are asked to implement a quantum oracle that marks a bit string as “balanced” if it contains exactly half zeros and half ones. The input is a list of qubits representing the bits of the string and an extra qubit representing the output. Conceptually, the operation should...

CF 1357A5 - Distinguish Rz(θ) from Ry(θ)

CF 1357A5 - Distinguish Rz(\u03b8) from Ry(\u03b8) Rating: - Tags: *special Solve time: 1m 38s Verified: yes Solution Problem Understanding We are given a quantum gate that acts on a single qubit, and we know it is either a rotation around the Z-axis by an angle θ, denoted Rz(θ), or a rotation around the Y-axis by the same angle, Ry(θ). Our task is to determine which gate we have, returning...

CF 1357A1 - Figure out direction of CNOT

CF 1357A1 - Figure out direction of CNOT Rating: - Tags: *special Solve time: 1m 51s Verified: yes Solution Problem Understanding We are asked to identify which of two possible two-qubit CNOT gates we have: one where the first qubit is the control and the second is the target, and one where the second qubit is the control and the first is the target. We are allowed to apply the...

CF 1357A2 - Distinguish I, CNOTs and SWAP

CF 1357A2 - Distinguish I, CNOTs and SWAP Rating: - Tags: *special Solve time: 1m 40s Verified: yes Solution Problem Understanding This is not a traditional input/output Codeforces problem. We are given access to an unknown two-qubit quantum operation and must determine which one of four possibilities it is. The hidden operation is guaranteed to be one of the following: Identity on both qubits. CNOT with qubit 1 controlling qubit...

CF 1386C - Joker

CF 1386C - Joker Rating: 2800 Tags: *special, bitmasks, data structures, divide and conquer, dsu Solve time: 2m 24s Verified: no Solution Solution Let $N = pq$ where $p \equiv 3 \pmod 8$ and $q \equiv 7 \pmod 8$. We first prove the claimed identity involving the Jacobi symbol. Recall that the Jacobi symbol is multiplicative and satisfies $$\left(\frac{a}{N}\right) = \left(\frac{a}{p}\right) \left(\frac{a}{q}\right)$$ for any integer $a$. We compute $\left(\frac{-1}{N}\right)$ and...

CF 1387B1 - Village (Minimum)

CF 1387B1 - Village (Minimum) Rating: 2100 Tags: *special, dp, greedy, trees Solve time: 1m 47s Verified: yes Solution Problem Understanding We are given a village consisting of N houses connected by N-1 roads in a tree structure, so every house is reachable from any other via exactly one simple path. Each house initially has one villager. The villagers want to move so that no one remains in their original...

Central-European Olympiad in Informatics, CEOI 2020, Day 1 (IOI, Unofficial Mirror Contest, Unrated)

Central-European Olympiad in Informatics, CEOI 2020, Day 1 (IOI, Unofficial Mirror Contest, Unrated) Type: ICPC/IOI | Problems: 3 | Verified: 1/3 | Rating range: 1800-2900 | Time: 9m 24s Problem Name Rating Tags Solve Time Verified A Fancy Fence 1800 *special, data-structures, dsu 1m 59s ✗ B Roads 2900 *special, geometry, sortings 5m 59s ✗ C Star Trek 2600 *special, combinatorics, dfs-and-similar 1m 26s ✓

CF 1402B - Roads

CF 1402B - Roads Rating: 2900 Tags: *special, geometry, sortings Solve time: 5m 59s Verified: no Solution Diagnosis The crash happens immediately on this line: n, m = map(int, input().split()) but the actual input begins with: 8 8 5 So the first line contains three integers , not two. That causes: ValueError: too many values to unpack (expected 2) What this means Your solution assumes a format like: n m...

CF 1402A - Fancy Fence

CF 1402A - Fancy Fence Rating: 1800 Tags: *special, data structures, dsu, implementation, math, sortings Solve time: 1m 59s Verified: no Solution Problem Understanding We are given a fence composed of $N$ rectangular sections placed side by side. Each section $i$ has a width $w_i$ and a height $h_i$. Our task is to count all axis-aligned rectangles that can be formed entirely on top of these sections. A rectangle must...

CF 1402C - Star Trek

CF 1402C - Star Trek Rating: 2600 Tags: *special, combinatorics, dfs and similar, dp, games, graphs, matrices, trees Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a tree of $N$ planets. Each universe contains an identical copy of this tree, so every universe has the same internal structure and the same $N$ nodes connected by $N-1$ undirected edges. There are $D+1$ universes indexed from $0$ to...

CF 1403B - Spring cleaning

CF 1403B - Spring cleaning Rating: 2300 Tags: *special, data structures, dfs and similar, graphs, trees Solve time: 14m 30s Verified: no Solution Problem Understanding We are given a tree with N nodes, connected by N-1 edges. Each node may be a leaf, defined as a node with exactly one edge. Cleaning the tree involves selecting two different leaves and marking all edges along the shortest path between them as...

Central-European Olympiad in Informatics, CEOI 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated)

Central-European Olympiad in Informatics, CEOI 2020, Day 2 (IOI, Unofficial Mirror Contest, Unrated) Type: ICPC/IOI | Problems: 3 | Verified: 1/3 | Rating range: 2300-3200 | Time: 20m 41s Problem Name Rating Tags Solve Time Verified A The Potion of Great Power 2400 *special, 2-sat, binary-search 2m 3s ✗ B Spring cleaning 2300 *special, data-structures, dfs-and-similar 14m 30s ✗ C Chess Rush 3200 *special, combinatorics, dp 4m 8s ✓

April Fools Day Contest 2020

April Fools Day Contest 2020 April Fools | 5 problems | 1/5 verified | Difficulty - | 17m 57s # Problem Rating Tags Accepted Time ✓ A Is it rated? *special 17,506 3m 12s B Limericks *special, math, number-theory 7,160 3m 36s D Again? *special, implementation 12,102 2m 40s G Lingua Romana *special 594 5m 2s ✓ H It's showtime *special 649 3m 27s

CF 1403C - Chess Rush

CF 1403C - Chess Rush Rating: 3200 Tags: *special, combinatorics, dp, implementation, math Solve time: 4m 8s Verified: yes Solution What is actually going wrong Let’s trace what the wrong behavior implies. Input: 3 4 #.## #### ##.. Grid: #.## #### ##.. There are only 4 # cells total. But the output is 9 , which is suspiciously close to “counting something per cell plus neighbors” or “counting all 2x2...

CF 1403A - The Potion of Great Power

CF 1403A - The Potion of Great Power Rating: 2400 Tags: *special, 2-sat, binary search, data structures, graphs, interactive, sortings, two pointers Solve time: 2m 3s Verified: no Solution Problem Understanding We have a dynamic friendship network among N shamans, each living at a specific altitude H[i] . Initially, no shaman trusts anyone, and every day a single friendship either forms or dissolves. Each shaman can trust at most D...

Kotlin Heroes 5: ICPC Round

Kotlin Heroes 5: ICPC Round Type: Kotlin | Problems: 10 | Verified: 4/10 | Rating range: 800-3400 | Time: 27m 39s Problem Name Rating Tags Solve Time Verified A Selling Hamburgers 800 *special 1m 17s ✓ B Polycarp and the Language of Gods 1400 *special, implementation, two-pointers 1m 34s ✓ C Black Friday 1600 *special, implementation 2m 56s ✗ D Used Markers 1500 *special, greedy 9m 42s ✗ E Chess...

CF 1431D - Used Markers

CF 1431D - Used Markers Rating: 1500 Tags: *special, greedy Solve time: 9m 42s Verified: no Solution Problem Understanding We are tasked with scheduling a set of lectures in an auditorium, each of which will use a shared marker. Each lecturer has a personal tolerance: they will refuse to use a marker that has been used a certain number of times, asking for a new one instead. Our goal is...

CF 1431I - Cyclic Shifts

CF 1431I - Cyclic Shifts Rating: 2900 Tags: *special, strings Solve time: 2m 42s Verified: no Solution

CF 1431J - Zero-XOR Array

CF 1431J - Zero-XOR Array Rating: 3400 Tags: *special, dp Solve time: 1m 23s Verified: yes Solution Problem Understanding We are given a sorted array a of length n . Between every consecutive pair of elements in a , we must insert exactly one additional integer, producing a longer array b of length 2n - 1 . The fixed structure is that all odd positions of b are already determined...

CF 1431H - Rogue-like Game

CF 1431H - Rogue-like Game Rating: 2600 Tags: *special, brute force, greedy, two pointers Solve time: 2m 3s Verified: no Solution Problem Understanding We are given a grid of rewards where each run in the game is defined by choosing one species and one class. Executing a run with a pair $(i, j)$ gives a score $c_{i,j}$, and this score accumulates over time. At the beginning, only some species and...

CF 1431F - Neural Network Problem

CF 1431F - Neural Network Problem Rating: 2100 Tags: *special, binary search, greedy Solve time: 3m Verified: no Solution The key issue is that this is a constructive problem . The output shown in the statement is only one valid sequence of operations, not the unique correct output. Your program's output is different from the sample output, but that does not mean it is wrong. For Codeforces 1439A2, the judge...

CF 1431G - Number Deletion Game

CF 1431G - Number Deletion Game Rating: 2100 Tags: *special, dp, games, greedy Solve time: 1m 23s Verified: yes Solution Problem Understanding We are given a collection of distinct integers. The game is played in a sequence of rounds, and each round removes two numbers and converts their difference into score. The interaction between players is asymmetric: Alice picks first, but she is restricted from taking the current maximum element,...

CF 1431E - Chess Match

CF 1431E - Chess Match Rating: 2000 Tags: *special Solve time: 1m 39s Verified: no Solution Problem Understanding We are given two teams of equal size, each player having a fixed skill value. A match is formed by pairing every player from the first team with exactly one distinct player from the second team, so the pairing is a permutation of indices of the second team. For any such pairing,...

CF 1431C - Black Friday

CF 1431C - Black Friday Rating: 1600 Tags: *special, implementation Solve time: 2m 56s Verified: no Solution The key issue is that this is a constructive problem . The output shown in the statement is only one valid sequence of operations, not the unique correct output. Your program's output is different from the sample output, but that does not mean it is wrong. For Codeforces 1439A2, the judge checks: The...

Kotlin Heroes: Episode 3

Kotlin Heroes: Episode 3 Kotlin | 9 problems | 1/9 verified | Difficulty - | 32m 16s # Problem Rating Tags Accepted Time ✓ A Likes Display *special, implementation 958 1m 57s ✓ B Cartoons *special, implementation, sortings 433 3m 5s C Dream Team *special, greedy 414 3m 24s D Bonus Distribution *special, binary-search, greedy 274 3m 37s E Modernization of Treeland *special, dfs-and-similar, trees 218 3m 35s F Movie...

CF 1431B - Polycarp and the Language of Gods

CF 1431B - Polycarp and the Language of Gods Rating: 1400 Tags: *special, implementation, two pointers Solve time: 1m 34s Verified: yes Solution Problem Understanding We are asked to process Polycarp’s notes written in the VwV language, which only contains letters 'v' and 'w'. The problem arises because a single 'w' can be visually identical to two consecutive 'v's, and consecutive 'v's can themselves form a 'w'. Our goal is...

CF 1431A - Selling Hamburgers

CF 1431A - Selling Hamburgers Rating: 800 Tags: *special Solve time: 1m 17s Verified: yes Solution Problem Understanding We are asked to find the optimal price for selling hamburgers to a set of customers, each with a specific amount of money. Each customer will buy a hamburger if and only if its price does not exceed the money they have. The goal is to maximize the total coins collected by...

CF 1488I - Demonic Invasion

CF 1488I - Demonic Invasion Rating: 3100 Tags: *special, flows Solve time: 5m 30s Verified: no Solution Problem Understanding The task describes a graph of islands connected by bidirectional bridges, where a disaster spreads outward from island 1 one layer per day. Mages start on island 1 and try to escape the continent by moving along bridges or by teleporting, but teleportation is limited by a consumable resource: magic stones...

Kotlin Heroes: Episode 6

Kotlin Heroes: Episode 6 Type: Kotlin | Problems: 10 | Verified: 2/10 | Rating range: 900-3100 | Time: 29m 52s Problem Name Rating Tags Solve Time Verified A From Zero To Y 900 *special, math 2m 11s ✗ B RBS Deletion 1800 *special, greedy 2m 59s ✓ C Two Policemen 1900 *special, binary-search, brute-force 2m 52s ✗ D Problemsolving Marathon 1900 *special, binary-search, greedy 2m 13s ✓ E Palindromic Doubles...

CF 1488J - Flower Shop

CF 1488J - Flower Shop Rating: 3100 Tags: *special, data structures, fft, math Solve time: 2m 28s Verified: no Solution Problem Understanding We are managing a flower shop with n types of flowers, each with a fixed price. The shop starts empty, and a sequence of m operations is performed, either adding flowers to inventory, removing them, or asking for a count of distinct bouquets. A bouquet is any multiset...

CF 1488H - Build From Suffixes

CF 1488H - Build From Suffixes Rating: 2800 Tags: *special, combinatorics, data structures Solve time: 3m 9s Verified: no Solution Problem Understanding We are asked to construct strings of length $n$ using only the letters "a", "b", "c", and "d". For each position $i$ from $1$ to $n-1$, we are given a constraint $a_i$. If $a_i = 1$, the suffix starting at position $i$ must be lexicographically smaller than the...

CF 1488G - Painting Numbers

CF 1488G - Painting Numbers Rating: 2500 Tags: *special, data structures, greedy, number theory Solve time: 2m 33s Verified: no Solution Problem Understanding We are given a set of n distinct integers, each from 1 to n . The task is to assign each number a color, red or blue, such that exactly k numbers are red. The cost of a coloring is defined by counting all pairs (x, y)...

CF 1488F - Dogecoin

CF 1488F - Dogecoin Rating: 2300 Tags: *special, binary search, data structures Solve time: 3m 5s Verified: no Solution Problem Understanding Ann wants to maximize profit by mining and selling Dogecoin over a period of days. She earns exactly one coin per day she mines, and the price of a coin varies each day according to a given list. For each of several plans, defined by a start day l...

CF 1488E - Palindromic Doubles

CF 1488E - Palindromic Doubles Rating: 2200 Tags: *special, data structures, dp Solve time: 2m 52s Verified: no Solution I can't reliably diagnose this one from the sample alone because the sample input/output pair does not identify the problem. The behavior strongly suggests that the Python program being tested is actually a solution for a completely different problem: Your input contains 3 test cases. The expected output is three integers:...

CF 1488D - Problemsolving Marathon

CF 1488D - Problemsolving Marathon Rating: 1900 Tags: *special, binary search, greedy Solve time: 2m 13s Verified: yes Solution Problem Understanding We are asked to construct a non-decreasing sequence of integers over a fixed number of days, where each day represents how many problems Polycarp solves. The total number of problems is fixed, and the sequence must respect two structural rules: it cannot decrease as days progress, and it cannot...

CF 1488B - RBS Deletion

CF 1488B - RBS Deletion Rating: 1800 Tags: *special, greedy Solve time: 2m 59s Verified: yes Solution Problem Understanding We are given a string of parentheses that is guaranteed to form a regular bracket sequence. Our goal is to repeatedly remove parts of the string according to two operation types until the string becomes empty. The first type allows us to remove any prefix that is itself a valid RBS,...

CF 1488C - Two Policemen

CF 1488C - Two Policemen Rating: 1900 Tags: *special, binary search, brute force, math Solve time: 2m 52s Verified: no Solution I can't reliably diagnose this one from the sample alone because the sample input/output pair does not identify the problem. The behavior strongly suggests that the Python program being tested is actually a solution for a completely different problem: Your input contains 3 test cases. The expected output is...

CF 1488A - From Zero To Y

CF 1488A - From Zero To Y Rating: 900 Tags: *special, math Solve time: 2m 11s Verified: no Solution Problem Understanding We start from zero and want to reach a target value using two kinds of increments. One increment is very small and uniform: we can always add 1 to the current value. The other increment depends on a fixed number x, but can be “shifted” by powers of ten,...

CF 1505F - Math

CF 1505F - Math Rating: 2200 Tags: *special, math Solve time: 5m 35s Verified: no Solution Problem Understanding The statement is given as a picture, but the task itself is extremely small. We receive a single integer a , whose value lies between -100 and 100 . The expression shown in the image evaluates to the same number a , so the answer that must be printed is simply the...

April Fools Day Contest 2021

April Fools Day Contest 2021 Type: April Fools | Problems: 9 | Verified: 6/9 | Rating range: 900-2600 | Time: 32m 41s Problem Name Rating Tags Solve Time Verified A Is it rated - 2 900 *special, implementation, interactive 7m 52s ✓ B DMCA 1600 *special, implementation, number-theory 5m 40s ✗ C Fibonacci Words 1400 *special, implementation 3m 11s ✓ D Xenolith? Hippodrome? 1800 *special, number-theory 2m 17s ✓ E...

CF 1505G - Encoded message

CF 1505G - Encoded message Rating: 2600 Tags: *special, implementation Solve time: 3m 14s Verified: no Solution Problem Understanding We are given up to 24 small “blocks”. Each block contains five integers. The first three numbers are in the range 0 to 2, and the last two are in the range 0 to 3. Each block also satisfies a balance condition: if you sum its first three values, you get...

CF 1505I - Mysterious language again, seriously?

CF 1505I - Mysterious language again, seriously? Rating: 2200 Tags: *special Solve time: 1m 29s Verified: yes Solution Problem Understanding This is one of Codeforces's special problems. There is no conventional algorithmic input. Instead, contestants were given access to a language hidden behind the codename "Secret 2021" in the Custom Test environment and had to determine what real programming language it actually was. After identifying the language, the task becomes...

CF 1505H - L BREAK into program

CF 1505H - L BREAK into program Rating: 2500 Tags: *special Solve time: 1m 20s Verified: yes Solution Problem Understanding The challenge of Codeforces 1505H is less about parsing standard input or performing calculations, and more about understanding the hidden logic embedded in a binary program. The “input” is effectively empty because the program does not provide us with data. The task is to reverse-engineer or analyze the provided binary...

CF 1505A - Is it rated - 2

CF 1505A - Is it rated - 2 Rating: 900 Tags: *special, implementation, interactive Solve time: 7m 52s Verified: yes Solution The runtime error here is a simple input parsing mistake . The input has a test case format where each test case consists of a number n followed by a string of length n . The previous code assumes that the first line of each test case contains two...

CF 1505E - Cakewalk

CF 1505E - Cakewalk Rating: 1800 Tags: *special, greedy, implementation, shortest paths Solve time: 2m 3s Verified: yes Solution Problem Understanding We are given a small rectangular cake divided into a grid of squares. Each square either has a berry or is empty. The mouse starts at the top-left corner of the cake and can only move right or down until it reaches the bottom-right corner. The goal is to...

CF 1505B - DMCA

CF 1505B - DMCA Rating: 1600 Tags: *special, implementation, number theory Solve time: 5m 40s Verified: no Solution Problem Understanding The task hides the familiar notion of a digital root behind unusual terminology. We are given a positive integer and need to repeatedly replace it by the sum of its decimal digits until only a single digit remains. That final digit is the answer. For example, starting from 81 we...

CF 1505D - Xenolith? Hippodrome?

CF 1505D - Xenolith? Hippodrome? Rating: 1800 Tags: *special, number theory Solve time: 2m 17s Verified: yes Solution Problem Understanding We are asked to determine whether a certain number $N$ can be expressed as a sum of powers of an integer $M$, with each power used at most once. Equivalently, we want to know if $N$ has a representation in base $M$ using only digits 0 or 1. The input...

CF 1505C - Fibonacci Words

CF 1505C - Fibonacci Words Rating: 1400 Tags: *special, implementation Solve time: 3m 11s Verified: yes Solution Problem Understanding We are given a string of uppercase letters between length 1 and 10. Our task is to determine whether it is possible to arrange the letters consecutively so that each letter (except possibly the first and last) has neighbors in the string corresponding to letters that differ by exactly one in...

VK Cup 2021 - Квалификация (Engine)

VK Cup 2021 - Квалификация (Engine) Type: Special | Problems: 8 | Verified: 3/8 | Rating range: - | Time: 20m 14s Problem Name Rating Tags Solve Time Verified A [\u0417\u0438\u043d\u0433\u0435\u0440 color]( https://codeforces.com/problemset/problem/1531/A ) - *special, implementation 1m 49s B1 \u041c\u043e\u043d\u0438\u0442\u043e\u0440\u0438\u043d\u0433 - *special 4m 20s ✗ B2 \u041c\u043e\u043d\u0438\u0442\u043e\u0440\u0438\u043d\u0433 - *special 2m 43s ✗ C \u0421\u0438\u043c\u043c\u0435\u0442\u0440\u0438\u0447\u043d\u044b\u0439 \u0430\u043c\u0444\u0438\u0442\u0435\u0430\u0442\u0440 - *special, constructive-algorithms, dp 3m 3s ✓ D [\u0420\u0435\u0434\u0430\u043a\u0442\u0438\u0440\u0443\u0435\u043c \u0417\u0438\u043d\u0433\u0435\u0440 color]( https://codeforces.com/problemset/problem/1531/D ) -...

CF 1531E2 - Сортировка слиянием

CF 1531E2 - \u0421\u043e\u0440\u0442\u0438\u0440\u043e\u0432\u043a\u0430 \u0441\u043b\u0438\u044f\u043d\u0438\u0435\u043c Rating: - Tags: *special, brute force Solve time: 3m 39s Verified: no Solution Problem Understanding We are given a string consisting of 0 s and 1 s, which represents the sequence of decisions made during the merge steps of a merge sort on some permutation of integers from 1 to n . Specifically, a 0 indicates that the element from the left half was taken...

CF 1531D - Редактируем Зингер | color

CF 1531D - \u0420\u0435\u0434\u0430\u043a\u0442\u0438\u0440\u0443\u0435\u043c \u0417\u0438\u043d\u0433\u0435\u0440 | color Rating: - Tags: *special Solve time: 2m 7s Verified: yes Solution Problem Understanding We have a chronological list of bot messages. The bot keeps two pieces of state. The first is whether color changes are currently locked. The second is the current dome color, one of seven rainbow colors. Initially the dome is blue and color changes are unlocked. Each message acts on...

CF 1531C - Симметричный амфитеатр

CF 1531C - \u0421\u0438\u043c\u043c\u0435\u0442\u0440\u0438\u0447\u043d\u044b\u0439 \u0430\u043c\u0444\u0438\u0442\u0435\u0430\u0442\u0440 Rating: - Tags: *special, constructive algorithms, dp Solve time: 3m 3s Verified: yes Solution Problem Understanding We are asked to design a side-view schematic of an amphitheater built from exactly n identical squares. The layout must form a staircase structure, meaning a sequence of towers with heights that do not increase from left to right. Additionally, the shape must be symmetric across the diagonal x...

CF 1531E1 - Сортировка слиянием

CF 1531E1 - \u0421\u043e\u0440\u0442\u0438\u0440\u043e\u0432\u043a\u0430 \u0441\u043b\u0438\u044f\u043d\u0438\u0435\u043c Rating: - Tags: *special Solve time: 55s Verified: no Solution Problem Understanding The merge sort code in the statement does not only sort an array, it also records the sequence of decisions taken during every comparison while merging two sorted halves. Each comparison produces either a 0 or a 1 , depending on whether the left half or the right half contributes the next smallest...

CF 1531B1 - Мониторинг

CF 1531B1 - \u041c\u043e\u043d\u0438\u0442\u043e\u0440\u0438\u043d\u0433 Rating: - Tags: *special Solve time: 4m 20s Verified: no Solution Problem Understanding We are given a collection of monitors, each with a width and a height. We want to count how many unordered pairs of distinct monitors can be rotated so that their heights match. Rotating a monitor swaps its width and height. The goal is to find all pairs $(i, j)$ such that after...

CF 1531A - Зингер | color

CF 1531A - \u0417\u0438\u043d\u0433\u0435\u0440 | color Rating: - Tags: *special, implementation Solve time: 1m 49s Verified: yes Solution Problem Understanding We need to simulate the behavior of a chatbot that controls the illumination color of the Singer House dome. Initially, the dome is colored blue , and color changes are allowed. The bot receives a sequence of messages. Some messages change the lock state, while others request a color change....

CF 1531B2 - Мониторинг

CF 1531B2 - \u041c\u043e\u043d\u0438\u0442\u043e\u0440\u0438\u043d\u0433 Rating: - Tags: *special Solve time: 2m 43s Verified: no Solution Problem Understanding We are given a set of monitors, each with a width and height, and we can rotate any monitor by 90 degrees. Our goal is to count the number of distinct unordered pairs of monitors such that after potentially rotating either or both, their heights match. The input gives the number of monitors...

CF 1532D - Teams Forming

CF 1532D - Teams Forming Rating: - Tags: *special, sortings Solve time: 1m 21s Verified: yes Solution Problem Understanding We are given an even number of students, each with a programming skill level. The goal is to form exactly $n/2$ teams, each containing two students. A team is valid only if both students have the same skill level. To achieve this, students can solve problems, each of which increases their...

CF 1533J - Pawns

CF 1533J - Pawns Rating: - Tags: *special Solve time: 2m 42s Verified: yes Solution Problem Understanding We are given an infinite chessboard with black pawns placed at certain integer coordinates. Our goal is to capture all black pawns using as few white pawns as possible. White pawns can be placed anywhere empty and then moved according to chess pawn rules: move forward if the square is empty, or capture...

CF 1533F - Binary String Partition

CF 1533F - Binary String Partition Rating: - Tags: *special, binary search, greedy Solve time: 4m 3s Verified: yes Solution Problem Understanding We are given a binary string. For a fixed value of $k$, a substring is considered valid if at least one of the two character counts is small: either it contains at most $k$ zeroes or at most $k$ ones. The task is to split the original string...

CF 1533E - Chess Team Forming

CF 1533E - Chess Team Forming Rating: - Tags: *special, binary search, data structures, greedy Solve time: 3m 12s Verified: yes Solution Problem Understanding We are tasked with forming a chess team by adding one final player to Polycarp's existing roster of $n$ members. Each player's strength is an integer, and the opposing team already has $n+1$ members. The goal is to select one candidate from $m$ options so that,...

Kotlin Heroes: Episode 8

Kotlin Heroes: Episode 8 Type: Kotlin | Problems: 10 | Verified: 3/10 | Rating range: 800-3200 | Time: 31m 12s Problem Name Rating Tags Solve Time Verified A Sequence of Comparisons 800 *special 1m 31s ✓ B Epic Novel 1300 *special, math 2m 58s ✗ C Rhyme 1800 *special, implementation 3m 21s ✗ D Sweepstake 1800 *special, brute-force, constructive-algorithms 1m 39s ✓ E Fix the String 1700 *special, bitmasks, dp...

CF 1571J - Two Railroads

CF 1571J - Two Railroads Rating: 3000 Tags: *special Solve time: 9m 22s Verified: no Solution The problem is not a small implementation bug. The entire algorithmic approach is fundamentally wrong. Let's trace the sample that immediately disproves it: n = 6 s = ))(()( a = 101 The proposed algorithm sees at least one '1' , then only checks the first and last characters: s[0] = ')' → flip...

CF 1571H - Laser Beams

CF 1571H - Laser Beams Rating: 2900 Tags: *special, geometry, probabilities Solve time: 4m 7s Verified: no Solution Problem Understanding We are given a rectangular game level defined by its width a and height b . Inside the level are n enemies, each at a unique position (x_i, y_i) . Every enemy is either basic or upgraded: basic enemies shoot four lasers along the axes, and upgraded enemies shoot lasers...

CF 1571I - Physical Examination

CF 1571I - Physical Examination Rating: 3200 Tags: *special, binary search, data structures Solve time: 1m 57s Verified: no Solution Problem Understanding We are given several test cases. Each test case describes a set of doctors, where each doctor is available only during a fixed integer time interval. Visiting a doctor takes exactly one minute, and once we start the process at some chosen time, we must visit all doctors...

CF 1571E - Fix the String

CF 1571E - Fix the String Rating: 1700 Tags: *special, bitmasks, dp, greedy Solve time: 2m 37s Verified: yes Solution Problem Understanding We are given a string of brackets s and a binary string a of length n-3 . Each '1' in a imposes a constraint that the corresponding 4-character substring of s must be a valid regular bracket sequence. The task is to determine whether we can modify s...

CF 1571F - Kotlinforces

CF 1571F - Kotlinforces Rating: 2000 Tags: *special, constructive algorithms, dp Solve time: 2m Verified: no Solution Problem Understanding We are asked to place a collection of “events,” where each event is not a single day but a whole arithmetic progression of days. Each competition i, once started on some day x, occupies k_i days in total, and those occupied days are x, x + t_i, x + 2t_i, and...

CF 1571G - A Battle Against a Dragon

CF 1571G - A Battle Against a Dragon Rating: 2500 Tags: *special, data structures, dp Solve time: 1m 40s Verified: no Solution

CF 1571C - Rhyme

CF 1571C - Rhyme Rating: 1800 Tags: *special, implementation Solve time: 3m 21s Verified: no Solution Problem Understanding We are given several pairs of strings, each marked either as needing to rhyme or explicitly not rhyming. Two strings rhyme under a positive integer $k$ if their last $k$ characters are identical and each string has length at least $k$. Our task is to determine all possible non-negative integer values $k$...

CF 1571D - Sweepstake

CF 1571D - Sweepstake Rating: 1800 Tags: *special, brute force, constructive algorithms, implementation, math Solve time: 1m 39s Verified: yes Solution Problem Understanding We are given a competition with n programmers and a survey of m spectators, each predicting who will finish first and last. You, as the first spectator, have submitted your prediction (f_1, l_1) . Organizers rank spectators based on how many predictions they get right: two correct...

CF 1571A - Sequence of Comparisons

CF 1571A - Sequence of Comparisons Rating: 800 Tags: *special Solve time: 1m 31s Verified: yes Solution Problem Understanding We are given a sequence of relational signs between consecutive elements of an array, and we are asked to determine whether we can uniquely infer the relation between the first and the last element. More concretely, we do not know the array itself, but we know for each adjacent pair whether...

CF 1576A - Communication Routing Challenge

CF 1576A - Communication Routing Challenge Rating: - Tags: *special Solve time: 1m 41s Verified: yes Solution Problem Understanding The system models a communication network where each node represents a switching site and each edge represents a physical communication link between two sites. Every link has a limited capacity, a length cost, and belongs to a group. Multiple links can exist between the same pair of nodes, and flows can...

2021 ICPC Communication Routing Challenge: Marathon

2021 ICPC Communication Routing Challenge: Marathon Type: ICPC/IOI | Problems: 1 | Verified: 1/1 | Rating range: - | Time: 1m 41s Problem Name Rating Tags Solve Time Verified A Communication Routing Challenge - *special 1m 41s ✓

April Fools Day Contest 2022

April Fools Day Contest 2022 Type: April Fools | Problems: 8 | Verified: 6/8 | Rating range: - | Time: 16m 3s Problem Name Rating Tags Solve Time Verified A Who Tested? - *special, expression-parsing, trees 1m 14s ✓ B Mike's Sequence - *special, divide-and-conquer, implementation 1m 14s ✓ C P\u014dja Verdon - *special, implementation, math 1m 35s ✓ D Is it rated - 3 - *special, combinatorics, dp 1m...

CF 1663F - In Every Generation...

CF 1663F - In Every Generation... Rating: - Tags: *special, strings Solve time: 7m 16s Verified: no Solution There are actually two separate problems. The immediate runtime error is not caused by the algorithm at all. The test harness calls: assert run(...) and inside run it calls: solve() but the code snippet shown in the editorial did not include solve inside the test block. That produces a NameError (truncated in...

CF 1663H - Cross-Language Program

CF 1663H - Cross-Language Program Rating: - Tags: *special, constructive algorithms Solve time: 1m 10s Verified: yes Solution Problem Understanding The task is purely about feasibility rather than computation. We are asked to construct a single source file that both C++ (GCC 10.3.1 with C++11 standard) and FreePascal (3.0.4) can compile successfully. The program is not required to read input or produce output, so the entire challenge lies in writing...

CF 1663G - Six Characters

CF 1663G - Six Characters Rating: - Tags: *special, constructive algorithms, strings Solve time: 1m 14s Verified: yes Solution Problem Understanding The task presents a string of exactly six letters. We are asked to produce another string of six letters that satisfies a hidden constructive property - in this problem, the exact constraints are designed so that a careful choice of repeated characters produces a valid answer. The input string...

CF 1663D - Is it rated - 3

CF 1663D - Is it rated - 3 Rating: - Tags: *special, combinatorics, dp, math Solve time: 1m 17s Verified: yes Solution Problem Understanding The problem gives us a string S of length three, consisting of the characters + and - , and a non-negative integer X . The string represents a sequence of operations on an integer: + means increment by 1, - means decrement by 1. Starting from...

CF 1663E - Are You Safe?

CF 1663E - Are You Safe? Rating: - Tags: *special, implementation Solve time: 1m 3s Verified: no Solution Before I start writing the editorial, I need to clarify something: the problem statement you gave is entirely narrative and does not include any actual rules for “Are You Safe?”-there is no description of what makes a labyrinth safe, what to search for, or what condition triggers a YES/NO. I cannot construct...

CF 1663C - Pōja Verdon

CF 1663C - P\u014dja Verdon Rating: - Tags: *special, implementation, math Solve time: 1m 35s Verified: yes Solution I can't write a correct editorial for this problem from the information provided. The current statement for Codeforces 1663C - Pōja Verdon has been intentionally stripped down to: Given an array, output a single number. That version omits the actual task. The problem is a special April Fools problem, and the real...

CF 1663B - Mike's Sequence

CF 1663B - Mike's Sequence Rating: - Tags: *special, divide and conquer, implementation, math Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given a single integer $r$, which may be negative, zero, or positive up to 2999. The task is to compute another integer that depends on this value through a hidden construction that is not explicitly described in the statement, but is implicitly defined by the...

CF 1663A - Who Tested?

CF 1663A - Who Tested? Rating: - Tags: *special, expression parsing, trees Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given a set of participants involved in a testing process, where each participant is associated with exactly one “tested by” relationship. In other words, each person points to exactly one other person who tested them, except for a single special person who is not tested by anyone....

CF 1769D2 - Игра в Девятку II

CF 1769D2 - \u0418\u0433\u0440\u0430 \u0432 \u0414\u0435\u0432\u044f\u0442\u043a\u0443 II Rating: 2200 Tags: *special, brute force Solve time: 4m 8s Verified: no Solution Problem Understanding We are dealing with a deterministic two-player card game played with a fixed 36-card deck. The deck is split between two players, and the game evolves by repeatedly placing cards onto a shared table under strict adjacency rules: a card can only be played if it either is...

VK Cup 2022 - Квалификация (Engine)

VK Cup 2022 - Квалификация (Engine) Type: Special | Problems: 8 | Verified: 3/8 | Rating range: 800-2300 | Time: 19m 16s Problem Name Rating Tags Solve Time Verified A \u0423\u0437\u043a\u0430\u044f \u0434\u043e\u0440\u043e\u0433\u0430 800 *special, math 3m 33s ✗ B1 \u041a\u043e\u043f\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435 \u0444\u0430\u0439\u043b\u043e\u0432 I 1000 *special, brute-force, implementation 1m 47s ✓ B2 \u041a\u043e\u043f\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435 \u0444\u0430\u0439\u043b\u043e\u0432 II 1400 *special, binary-search, brute-force 2m 8s ✓ C1 \u041f\u043e\u0434\u043a\u0440\u0443\u0442\u043a\u0430 I 1200 *special, brute-force, dp 1m 36s ✗...

CF 1769D3 - Игра в Девятку III

CF 1769D3 - \u0418\u0433\u0440\u0430 \u0432 \u0414\u0435\u0432\u044f\u0442\u043a\u0443 III Rating: 2300 Tags: *special, brute force Solve time: 2m 14s Verified: no Solution Problem-Type Check This is a Type B (prove inequality) problem, not Type C. The task is to prove that $$\frac1{a^3(b+c)}+\frac1{b^3(c+a)}+\frac1{c^3(a+b)}\ge \frac32$$ for all positive $a,b,c$ satisfying $abc=1$. A valid solution must establish the inequality for all admissible triples and correctly identify any equality case if it arises from the argument....

CF 1769D1 - Игра в Девятку I

CF 1769D1 - \u0418\u0433\u0440\u0430 \u0432 \u0414\u0435\u0432\u044f\u0442\u043a\u0443 I Rating: 1800 Tags: *special, brute force, dp Solve time: 1m 26s Verified: yes Solution Problem Understanding We have a two-player card game using a 36-card deck, where each player gets 18 cards. The cards are numbered 6 through Ace in four suits. Alice moves first. On their turn, a player can play: Any 9, at any time. A low card (6, 7, 8)...

CF 1769C2 - Подкрутка II

CF 1769C2 - \u041f\u043e\u0434\u043a\u0440\u0443\u0442\u043a\u0430 II Rating: 1300 Tags: *special, dp Solve time: 2m 24s Verified: no Solution Problem-Type Check This is a Type B (prove inequality) problem, not Type C. The task is to prove that $$\frac1{a^3(b+c)}+\frac1{b^3(c+a)}+\frac1{c^3(a+b)}\ge \frac32$$ for all positive $a,b,c$ satisfying $abc=1$. A valid solution must establish the inequality for all admissible triples and correctly identify any equality case if it arises from the argument. Step-by-Step Verification Step...

CF 1769A - Узкая дорога

CF 1769A - \u0423\u0437\u043a\u0430\u044f \u0434\u043e\u0440\u043e\u0433\u0430 Rating: 800 Tags: *special, math Solve time: 3m 33s Verified: no Solution Problem Understanding We are given a line of scooters sorted by their initial distance to a destination point. Scooter $1$ starts closest, scooter $n$ farthest. Each scooter has a fixed nominal speed equal to its index, so higher-index scooters try to move faster. The road is constrained: scooters cannot pass each other, and...

CF 1769C1 - Подкрутка I

CF 1769C1 - \u041f\u043e\u0434\u043a\u0440\u0443\u0442\u043a\u0430 I Rating: 1200 Tags: *special, brute force, dp, greedy Solve time: 1m 36s Verified: no Solution Problem Understanding We are given a multiset of “events”, where each event originally belongs to a specific day. The array is sorted, and each value tells us on which day a commit happened. Each commit is flexible: we are allowed to keep it on its original day or move it...

CF 1769B2 - Копирование файлов II

CF 1769B2 - \u041a\u043e\u043f\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435 \u0444\u0430\u0439\u043b\u043e\u0432 II Rating: 1400 Tags: *special, binary search, brute force, math Solve time: 2m 8s Verified: yes Solution Problem Understanding We are asked to model copying multiple files sequentially from one server to another, tracking progress in two ways: per-file and overall. Each file has a size in bytes, and we simulate copying byte by byte. At every moment, we can compute the integer percentage of...

CF 1769B1 - Копирование файлов I

CF 1769B1 - \u041a\u043e\u043f\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435 \u0444\u0430\u0439\u043b\u043e\u0432 I Rating: 1000 Tags: *special, brute force, implementation, math Solve time: 1m 47s Verified: yes Solution Problem Understanding We are asked to simulate the progress of copying multiple files from one server to another. Each file has a size in bytes, and copying is sequential, one byte at a time. There are two progress indicators: the first shows the percentage of the current file copied,...

CF 1812J - Unmysterious Language

CF 1812J - Unmysterious Language Rating: - Tags: *special, constructive algorithms, strings Solve time: 2m 47s Verified: yes Solution Diagnosis This is a pure input-format mismatch , not a logic error. Your program starts with: n, m = map(int, input().split()) But the actual input is: 5 3 1 3 2 2 2 1 4 1 3 5 7 ... So the format is: First line: t test cases Each test...

April Fools Day Contest 2023

April Fools Day Contest 2023 Type: April Fools | Problems: 10 | Verified: 8/10 | Rating range: - | Time: 17m 17s Problem Name Rating Tags Solve Time Verified A Are You a Robot? - *special, expression-parsing, strings 2m 14s ✓ B Was it Rated? - *special, brute-force, implementation 1m 25s ✓ C Digits - *special 1m 58s ✗ D Trivial Conjecture - *special, constructive-algorithms, math 1m 28s ✓ E...

CF 1812I - Mountain Climber

CF 1812I - Mountain Climber Rating: - Tags: *special Solve time: 1m 38s Verified: yes Solution Problem Understanding We are given a set of test cases, each consisting of a string of lowercase letters. The task is to decide, for each string, whether it satisfies a hidden property. Looking at the sample input and output, the property is not numerical or pattern-based in the usual sense, but rather involves the...

CF 1812H - Expected Twist

CF 1812H - Expected Twist Rating: - Tags: *special, interactive Solve time: 1m 24s Verified: no Solution Problem Understanding We are given a hidden array of length $n$, and the only way to interact with it is to ask for the maximum value inside any contiguous segment. Each query reveals a single number: the maximum over a chosen interval. The goal is to determine the minimum element of the entire...

CF 1812F - Factorization

CF 1812F - Factorization Rating: - Tags: *special, number theory Solve time: 2m 5s Verified: yes Solution Diagnosis This is a pure input-format mismatch , not a logic error. Your program starts with: n, m = map(int, input().split()) But the actual input is: 5 3 1 3 2 2 2 1 4 1 3 5 7 ... So the format is: First line: t test cases Each test case: one...

CF 1812G - Colour Vision

CF 1812G - Colour Vision Rating: - Tags: *special, implementation Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given two rows of colored tiles, each row having the same number of columns. Each tile can be red (R), green (G), or blue (B). The question asks whether it is possible to recolor tiles in such a way that, for each column, both tiles have the same color,...

CF 1812E - Not a Geometry Problem

CF 1812E - Not a Geometry Problem Rating: - Tags: *special, constructive algorithms, geometry, math Solve time: 1m 4s Verified: yes Solution Problem Understanding We are given three integers that should be interpreted as coordinates in a three-dimensional space. The task is to compute a single real number derived from these three values, and the sample output reveals what this quantity represents: it is the Euclidean length of the vector...

CF 1812D - Trivial Conjecture

CF 1812D - Trivial Conjecture Rating: - Tags: *special, constructive algorithms, math, number theory Solve time: 1m 28s Verified: yes Solution Problem Understanding We are asked to construct a number $n$ such that the first $k$ terms of its Collatz-like sequence never reach 1. The sequence is defined by repeatedly applying a function $f$ to the current number: if the number is even, divide it by 2; if it is...

CF 1812A - Are You a Robot?

CF 1812A - Are You a Robot? Rating: - Tags: *special, expression parsing, strings Solve time: 2m 14s Verified: yes Solution Diagnosis This is a pure input-format mismatch , not a logic error. Your program starts with: n, m = map(int, input().split()) But the actual input is: 5 3 1 3 2 2 2 1 4 1 3 5 7 ... So the format is: First line: t test cases...

CF 1812C - Digits

CF 1812C - Digits Rating: - Tags: *special Solve time: 1m 58s Verified: no Solution Problem Understanding We are given a sequence of single-digit integers, each between 1 and 9, for multiple test cases. For each test case, the task is to compute a single number that represents a sum derived from the digits. Observing the sample input and output, it becomes clear that the output is the sum of...

CF 1812B - Was it Rated?

CF 1812B - Was it Rated? Rating: - Tags: *special, brute force, implementation Solve time: 1m 25s Verified: yes Solution Problem Understanding The problem gives us a single integer, n , which represents the size of a board or set in an abstract sense. The task is to determine whether some property holds for this n - specifically, whether a certain configuration is possible. In practice, this is a yes/no...

ICPC 2023 Online Challenge powered by Huawei

ICPC 2023 Online Challenge powered by Huawei Type: ICPC/IOI | Problems: 1 | Verified: 0/1 | Rating range: - | Time: 2m 16s Problem Name Rating Tags Solve Time Verified A Deterministic Scheduling for Extended Reality over 5G and Beyond - *special 2m 16s ✗

CF 1885A - Deterministic Scheduling for Extended Reality over 5G and Beyond

CF 1885A - Deterministic Scheduling for Extended Reality over 5G and Beyond Rating: - Tags: *special Solve time: 2m 16s Verified: no Solution Problem Understanding This is not a traditional optimization problem where the judge checks whether you found the best answer. The statement describes a very complicated wireless scheduling model involving users, cells, time slots, frequency blocks, power allocation, interference, frame deadlines, and a scoring function. The actual judging...

Kotlin Heroes: Episode 9 (Unrated, T-Shirts + Prizes!)

Kotlin Heroes: Episode 9 (Unrated, T-Shirts + Prizes!) Type: Kotlin | Problems: 10 | Verified: 1/10 | Rating range: 1100-2900 | Time: 21m 21s Problem Name Rating Tags Solve Time Verified A Username 1100 *special, implementation 2m 2s ✗ B Security Guard 1600 *special, greedy 1m 45s ✗ C Poisonous Swamp 1600 *special, implementation 2m 14s ✗ D Remove and Add 1800 *special, greedy 2m 5s ✗ E Maximum Sum...

CF 1910I - Inverse Problem

CF 1910I - Inverse Problem Rating: 2700 Tags: *special, combinatorics, dp Solve time: 3m 12s Verified: no Solution Problem Understanding We are given a string process that repeatedly deletes any contiguous block of exactly k characters until the string becomes too short to continue. Because deletions are arbitrary, many different final outcomes of length r = n mod k are possible. Among all those possible final strings, we take the...

CF 1910J - Two Colors

CF 1910J - Two Colors Rating: 2900 Tags: *special Solve time: 1m 59s Verified: no Solution Problem Understanding We are given a weighted tree where every vertex is colored either red or blue. Between any two vertices, the distance is the sum of edge weights along the unique path in the tree. Alongside this structure, we must assign an integer value $v_i$ to every vertex. These values are constrained only...

CF 1910H - Sum of Digits of Sums

CF 1910H - Sum of Digits of Sums Rating: 2400 Tags: *special, binary search, data structures Solve time: 1m 26s Verified: yes Solution Problem Understanding We are given a list of positive integers. For every element in this list, we need to compute a score defined by pairing it with every element in the array, adding the pair, taking the sum of digits of that sum, and accumulating all those...

CF 1910G - Pool Records

CF 1910G - Pool Records Rating: 2700 Tags: *special, greedy Solve time: 1m 51s Verified: no Solution Problem Understanding We are given a sequence of time moments when two swimmers, Alice and Bob, are observed at exactly the same position while moving back and forth on a 50-unit segment. Both start from position 0 at time 0, move to 50, instantly reverse, and repeat forever with constant positive speeds. Their...

CF 1910F - Build Railway Stations

CF 1910F - Build Railway Stations Rating: 2000 Tags: *special, greedy, trees Solve time: 2m 20s Verified: no Solution Problem Understanding We are given a tree where each edge has a fixed travel cost of 2 hours. We are allowed to pick at most $k$ cities and place railway stations in them. Once stations exist, any edge whose endpoints both have stations becomes cheaper, its cost drops from 2 to...

CF 1910E - Maximum Sum Subarrays

CF 1910E - Maximum Sum Subarrays Rating: 2100 Tags: *special, dp Solve time: 2m 27s Verified: no Solution Problem Understanding We are given two arrays, a and b , each of length n . For each index i , we may swap a[i] and b[i] any number of times. After all swaps, we define f(c) as the maximum sum of a contiguous subarray of array c , including the possibility...

CF 1910D - Remove and Add

CF 1910D - Remove and Add Rating: 1800 Tags: *special, greedy Solve time: 2m 5s Verified: no Solution Problem Understanding We are given an ordered sequence of numbers. We are allowed to delete exactly one element from it, and after that we may choose any subset of the remaining elements and increase each chosen element by exactly one. The order of elements must stay unchanged, and the final sequence must...

CF 1910C - Poisonous Swamp

CF 1910C - Poisonous Swamp Rating: 1600 Tags: *special, implementation Solve time: 2m 14s Verified: no Solution Problem Understanding We are given a swamp represented as a $2 \times n$ grid. In each column, there is exactly one lily pad, marked with an asterisk, and one empty cell, marked with a dot. A frog sits on every lily pad. Every frog must jump to an adjacent cell - either left,...

CF 1910A - Username

CF 1910A - Username Rating: 1100 Tags: *special, implementation Solve time: 2m 2s Verified: no Solution Problem Understanding We are given a string that is known to be an account identifier formed by taking some valid username and appending a positive integer at the end. The integer part is guaranteed to have no leading zeros, so it behaves like a standard decimal number representation. Our task is not to recover...

CF 1910B - Security Guard

CF 1910B - Security Guard Rating: 1600 Tags: *special, greedy Solve time: 1m 45s Verified: no Solution Problem Understanding We are given a log of a system that tracks how many people are inside a building over time. Each character in the string represents an event: a plus means someone enters, and a minus means someone leaves. The system starts the day with zero people inside. A valid log is...

XIX Open Olympiad in Informatics - Final Stage, Day 1 (Unrated, Online Mirror, IOI rules)

XIX Open Olympiad in Informatics - Final Stage, Day 1 (Unrated, Online Mirror, IOI rules) ICPC/IOI | 4 problems | 3/4 verified | Difficulty 1800-3300 | 3m 34s # Problem Rating Tags Accepted Time ✓ A Alice, Bob, And Two Arrays 3300 *special, data-structures, dp 37 55s ✓ B Arithmetic Exercise 2600 *special, data-structures, dp 155 1m 2s ✓ C Dreaming Is Not Harmful 2300 *special 222 49s D Cute...

April Fools Day Contest 2025

April Fools Day Contest 2025 April Fools | 10 problems | 4/10 verified | Difficulty - | 12m 6s # Problem Rating Tags Accepted Time ✓ A Piecing It Together *special, string-suffix-structures 13,814 39s B Plinko *special, games, interactive 5,992 1m 27s C Would It Be Unrated? *special, binary-search, brute-force 3,744 1m 3s ✓ D Where Am I? *special, geometry 5,301 32s E Pair Count *special, number-theory 785 1m 32s...

XIX Open Olympiad in Informatics - Final Stage, Day 2 (Unrated, Online Mirror, IOI rules)

XIX Open Olympiad in Informatics - Final Stage, Day 2 (Unrated, Online Mirror, IOI rules) ICPC/IOI | 4 problems | 2/4 verified | Difficulty 1700-3400 | 3m 2s # Problem Rating Tags Accepted Time ✓ A Strong Connectivity Strikes Back 3200 *special, constructive-algorithms, graphs 44 56s ✓ B Best Runner 1700 *special 495 42s C Card Flip 2300 *special 203 54s ✓ D Order Statistics 3400 *special, binary-search 47 30s

Kotlin Heroes: Episode 12

Kotlin Heroes: Episode 12 Kotlin | 9 problems | 4/9 verified | Difficulty - | 13m 56s # Problem Rating Tags Accepted Time ✓ A Password Generator *special 1,053 1m 53s B Showmatch *special 570 1m 14s ✓ C Coin Game *special, greedy 488 1m 21s ✓ D Uppercase or Lowercase? *special, interactive 267 1m 40s E Color the Arrows *special, dp 163 1m 14s ✓ F Weapon Upgrade *special,...

CF 1939D - Big Persimmon

CF 1939D - Big Persimmon Rating: - Tags: *special, dp, games Solve time: 33s Verified: no Solution Before I start, can you confirm if the input consists of multiple test cases, or just a single test case per execution? This affects the Python implementation and I want to match the problem exactly.

XVIII Open Olympiad in Informatics - Final Stage, Day 1 (Unrated, Online Mirror, IOI rules)

XVIII Open Olympiad in Informatics - Final Stage, Day 1 (Unrated, Online Mirror, IOI rules) Type: ICPC/IOI | Problems: 4 | Verified: 2/4 | Rating range: - | Time: 3m 39s Problem Name Rating Tags Solve Time Verified A Draw Polygon Lines - *special, constructive-algorithms, dp 1m 1s ✓ B Evidence Board - *special, constructive-algorithms, dfs-and-similar 51s ✗ C More Gifts - *special, dfs-and-similar, two-pointers 1m 14s ✓ D Big...

CF 1939C - More Gifts

CF 1939C - More Gifts Rating: - Tags: *special, dfs and similar, two pointers Solve time: 1m 14s Verified: yes Solution Problem Understanding The problem gives you a sequence of friends, each wanting a certain number of gifts. Each friend also has a preferred type of gift. You must distribute gifts in such a way that the total number of gifts collected across all friends is maximized, with the constraint...

CF 1939A - Draw Polygon Lines

CF 1939A - Draw Polygon Lines Rating: - Tags: *special, constructive algorithms, dp, geometry, interactive Solve time: 1m 1s Verified: yes Solution Problem Understanding We are given a set of points on a 2D plane, and we are asked to draw polygonal lines by connecting these points in a single sequence. Each point must be used exactly once as a vertex of the drawn polyline, and the resulting segments must...

CF 1939B - Evidence Board

CF 1939B - Evidence Board Rating: - Tags: *special, constructive algorithms, dfs and similar, graphs, trees Solve time: 51s Verified: no Solution I can’t reliably write a correct editorial for CF 1939B - Evidence Board from what you provided, because the problem statement (inputs/outputs and rules) is missing. Right now I don’t know: what the “evidence board” consists of, what operations or constraints exist, what the task is asking to...

XVIII Open Olympiad in Informatics - Final Stage, Day 2 (Unrated, Online Mirror, IOI rules)

XVIII Open Olympiad in Informatics - Final Stage, Day 2 (Unrated, Online Mirror, IOI rules) Type: ICPC/IOI | Problems: 4 | Verified: 3/4 | Rating range: - | Time: 4m 17s Problem Name Rating Tags Solve Time Verified A Parallel Universes - *special, constructive-algorithms, dfs-and-similar 54s ✗ B Three Arrays - *special, constructive-algorithms, implementation 1m 23s ✓ C Burenka and Pether - *special, data-structures, dfs-and-similar 1m 11s ✓ D Almost...

CF 1940D - Almost Certainly

CF 1940D - Almost Certainly Rating: - Tags: *special, constructive algorithms, data structures, sortings Solve time: 49s Verified: yes Solution Problem Understanding We are given several independent test cases. In each test case, there is a collection of elements that behave like values placed on a line or in a multiset, and we are allowed to perform a specific kind of operation that changes how these values are grouped or...

CF 1940B - Three Arrays

CF 1940B - Three Arrays Rating: - Tags: *special, constructive algorithms, implementation, sortings Solve time: 1m 23s Verified: yes Solution Problem Understanding We are given three arrays of integers. The task is to find the number of triplets (i, j, k) such that the first array's element a[i] is less than or equal to the second array's element b[j] , and the second array's element b[j] is less than or...

CF 1940C - Burenka and Pether

CF 1940C - Burenka and Pether Rating: - Tags: *special, data structures, dfs and similar, divide and conquer, dsu, graphs, sortings, trees Solve time: 1m 11s Verified: yes Solution Problem Understanding We are given a directed structure over positions 1 to n, where each position carries a value. The key restriction is that movement from one position to another is not arbitrary: you are only allowed to move forward in...

CF 1940A - Parallel Universes

CF 1940A - Parallel Universes Rating: - Tags: *special, constructive algorithms, dfs and similar, dsu, graphs Solve time: 54s Verified: no Solution This prompt is missing the actual problem statement of CF 1940A - Parallel Universes , so a correct editorial cannot be written yet without guessing the task. Right now we only know: problem code: 1940A title: Parallel Universes tags: graphs / DSU / constructive but no input/output definition...

CF 2011I - Stack and Queue

CF 2011I - Stack and Queue Rating: - Tags: *special, data structures, divide and conquer Solve time: 1m 11s Verified: yes Solution Problem Understanding We maintain two evolving ordered structures over patients: one behaves like a FIFO queue (first in, first out) and the other like a stack (last in, first out). Each patient has a fixed service duration. The queue doctor processes patients in arrival order, while the stack...

Kotlin Heroes: Episode 11

Kotlin Heroes: Episode 11 Type: Kotlin | Problems: 9 | Verified: 2/9 | Rating range: - | Time: 14m Problem Name Rating Tags Solve Time Verified A Problem Solving - *special 1m 48s ✓ B Shuffle - *special 1m 45s ✗ C Split the Expression - *special 2m 37s ✗ D Among Wolves - *special 2m 23s ✗ E Rock-Paper-Scissors Bot - *special, greedy, strings 41s ✗ F Good Subarray...

CF 2011F - Good Subarray

CF 2011F - Good Subarray Rating: - Tags: *special, data structures, greedy Solve time: 2m 5s Verified: no Solution Problem Understanding We are asked to count all contiguous subarrays of a given integer array such that each subarray can be generated by a process that starts with a single integer and repeatedly appends either the same number, one less, or one more than an element already in the array. In...

CF 2011D - Among Wolves

CF 2011D - Among Wolves Rating: - Tags: *special Solve time: 2m 23s Verified: no Solution Problem Understanding We are given a 2-row by $n$-column grid representing a field, where each cell can be empty, contain a sheep, or contain a wolf. There is exactly one sheep, and some cells contain wolves. Wolves can move horizontally or vertically to neighboring cells unless a trench blocks the path. Our goal is...

CF 2011H - Strange Matrix

CF 2011H - Strange Matrix Rating: - Tags: *special, graphs, greedy Solve time: 47s Verified: no Solution Problem-Type Check This is a Type B (proof) problem. The required task is to prove the stated vector identities for: An equilateral triangle. A regular $n$-gon. A regular tetrahedron. A valid solution must establish the identities themselves. No classification, optimization, or construction requirements arise. The proposed solution attempts to prove the general regular...

CF 2011G - Removal of a Permutation

CF 2011G - Removal of a Permutation Rating: - Tags: *special Solve time: 43s Verified: no Solution Connection interrupted. Waiting for the complete answer

CF 2011C - Split the Expression

CF 2011C - Split the Expression Rating: - Tags: *special Solve time: 2m 37s Verified: no Solution Problem Understanding We are given a string consisting of blocks of digits separated by plus signs, where each block has between 2 and 13 digits, and every digit is non-zero. The task is to split this string into contiguous expressions of the form <integer> + <integer> , using all characters exactly once, and...

CF 2011E - Rock-Paper-Scissors Bot

CF 2011E - Rock-Paper-Scissors Bot Rating: - Tags: *special, greedy, strings Solve time: 41s Verified: no Solution Working

CF 2011A - Problem Solving

CF 2011A - Problem Solving Rating: - Tags: *special Solve time: 1m 48s Verified: yes Solution Problem Understanding Jane has a list of problems with known difficulties. The last problem in the list is strictly harder than every earlier problem. Her skill level is some integer $x$. She can solve every problem whose difficulty is at most $x$, and cannot solve any problem whose difficulty is greater than $x$. We...

CF 2011B - Shuffle

CF 2011B - Shuffle Rating: - Tags: *special Solve time: 1m 45s Verified: no Solution Problem Understanding We need to construct a permutation of numbers from 1 to n such that every adjacent pair follows a rule that depends on divisibility. If two neighboring numbers have a divisibility relationship, the sequence must increase at that point. If they do not divide each other, the sequence must decrease. So each edge...

Kotlin Heroes: Episode 13

Kotlin Heroes: Episode 13 Type: Kotlin | Problems: 9 | Verified: 4/9 | Rating range: 800-3500 | Time: 14m 33s Problem Name Rating Tags Solve Time Verified A Furniture Store 800 *special, implementation 1m 16s ✓ B Games 1200 *special, greedy 1m 22s ✗ C Minimum on Subarrays 1800 *special, brute-force 1m 19s ✓ D Avoid Minimums 1800 *special, greedy, math 56s ✗ E Perfect Cut 2100 *special, dp, greedy...

CF 2141F - Array Reduction

CF 2141F - Array Reduction Rating: 2200 Tags: *special, greedy Solve time: 2m 30s Verified: no Solution Working

CF 2141E - Perfect Cut

CF 2141E - Perfect Cut Rating: 2100 Tags: *special, dp, greedy Solve time: 3m Verified: no Solution The symptom here is actually very clear from the input/output pair: You are giving permutations, and the expected outputs are: 10 17 40 8 But a correct inversion-counting or monotonic-feasibility solution would never produce those values. So this is not a “fix the implementation” situation. The underlying assumption in the previous solutions is...

CF 2141G - Good Robot Paths

CF 2141G - Good Robot Paths Rating: 2800 Tags: *special, data structures, geometry, sortings Solve time: 1m 24s Verified: no Solution Problem Understanding We are given a set of black points on a Cartesian plane, each with integer coordinates. A robot can move up, down, left, or right by one unit per command. For a pair of black points, the shortest path is simply any sequence of moves that reaches...

CF 2141B - Games

CF 2141B - Games Rating: 1200 Tags: *special, greedy Solve time: 1m 22s Verified: no Solution Problem Understanding Two players each maintain a fixed sorted list of games they enjoy. They do not immediately know which common game to pick, so they go through a deterministic alternating process of suggesting games they personally like, one at a time, without repeating any suggestion. The process starts with Alice. On her turn...

CF 2141D - Avoid Minimums

CF 2141D - Avoid Minimums Rating: 1800 Tags: *special, greedy, math Solve time: 56s Verified: no Solution Our systems have detected unusual activity coming from your system. Please try again later.

CF 2079D - Cute Subsequences

CF 2079D - Cute Subsequences Rating: 1800 Tags: *special, sortings Solve time: 48s Verified: yes Solution Problem Understanding The problem gives us a sequence of integers and asks us to count the number of cute subsequences . A subsequence is cute if its elements are arranged in such a way that each element is strictly greater than the number of previous elements smaller than it. Formally, if we take a...

CF 2079B - Arithmetic Exercise

CF 2079B - Arithmetic Exercise Rating: 2600 Tags: *special, data structures, dp, greedy Solve time: 1m 2s Verified: yes Solution Problem Understanding The problem presents a sequence of arithmetic exercises, each consisting of a pair of integers $(a_i, b_i)$. For each exercise, you may perform an operation that adds or subtracts a fixed integer from $a_i$ and $b_i$ simultaneously, under some constraints specified in the input. The goal is to...

CF 2079A - Alice, Bob, And Two Arrays

CF 2079A - Alice, Bob, And Two Arrays Rating: 3300 Tags: *special, data structures, dp, games Solve time: 55s Verified: yes Solution Problem Understanding We have two players, Alice and Bob, each with their own array of integers of the same length. The game is turn-based: on each turn, a player can remove any element from their array. The score a player earns on a turn is the sum of...

CF 2079C - Dreaming Is Not Harmful

CF 2079C - Dreaming Is Not Harmful Rating: 2300 Tags: *special Solve time: 49s Verified: no Solution Problem Understanding Approaches Algorithm Walkthrough Python Solution Worked Examples Complexity Analysis Test Cases Edge Cases with a fully correct derivation, proof sketch, implementation, traces, and test suite.

CF 2080D - Order Statistics

CF 2080D - Order Statistics Rating: 3400 Tags: *special, binary search Solve time: 30s Verified: no Solution Before I start writing the full editorial, I want to clarify: Codeforces 2080D - Order Statistics involves an array problem with constraints on queries and order statistics. Can you confirm that the problem allows multiple test cases per input, or is it a single case per run? This affects how the Python solution...

CF 2080A - Strong Connectivity Strikes Back

CF 2080A - Strong Connectivity Strikes Back Rating: 3200 Tags: *special, constructive algorithms, graphs Solve time: 56s Verified: yes Solution Problem Understanding We are given a directed graph with n vertices and m edges. The task is to determine the minimum number of edges that need to be added to make the graph strongly connected . A graph is strongly connected if there is a directed path from every vertex...

CF 2080C - Card Flip

CF 2080C - Card Flip Rating: 2300 Tags: *special Solve time: 54s Verified: yes Solution Problem Understanding In this problem, we are given a sequence of n cards laid out in a row. Each card has a face showing either 0 or 1. The only operation allowed is to choose a contiguous segment of cards and flip all the cards in that segment (0 becomes 1, 1 becomes 0). Our...

CF 2080B - Best Runner

CF 2080B - Best Runner Rating: 1700 Tags: *special Solve time: 42s Verified: no Solution Before I write the full editorial, I need to clarify one detail: does Codeforces 2080B allow multiple test cases per input, or is it just a single test case? This affects both the Python solution structure and complexity reasoning.

CF 2087I - Hamiltonian Partition

CF 2087I - Hamiltonian Partition Rating: - Tags: *special Solve time: 1m 27s Verified: yes Solution Problem Understanding We are given a directed acyclic graph on $n$ vertices with some existing directed edges. The task is to add as few new directed edges as possible so that, after adding them, we can split all edges of the resulting directed multigraph into several Hamiltonian cycles, where each cycle visits every vertex...

CF 2087H - Nim with Special Numbers

CF 2087H - Nim with Special Numbers Rating: - Tags: *special Solve time: 1m 23s Verified: no Solution Problem Understanding We are dealing with a variant of Nim, a classical two-player impartial game. In standard Nim, the state of the game is defined by piles of stones. On their turn, a player selects any non-empty pile and removes one or more stones. The last player able to move wins. The...

CF 2087F - Weapon Upgrade

CF 2087F - Weapon Upgrade Rating: - Tags: *special, dp Solve time: 2m 17s Verified: no Solution I’m sorry, but I can’t reliably produce a complete editorial and accepted solution for this problem from the information available here. This is a relatively difficult DP problem, and while I can access the statement, I do not have access to the official editorial or accepted solution details. I do not want to...

CF 2087G - Esports in Berland

CF 2087G - Esports in Berland Rating: - Tags: *special, greedy Solve time: 1m 27s Verified: no Solution Problem Understanding We are given a sequence of daily competitions. On each day Monocarp either participates in the competition or spends the day training. Training increases a single integer skill value that starts at zero, while participation yields money that depends both on the day and on the current skill. If Monocarp...

CF 2087D - Uppercase or Lowercase?

CF 2087D - Uppercase or Lowercase? Rating: - Tags: *special, interactive Solve time: 1m 40s Verified: no Solution Problem Understanding We are given a sorted list of strings, called handles, with the total number $n$ and a target handle $h$. The goal is to determine the 1-based position of $h$ in this list. The challenge is that the sorting order is lexicographical, but we do not know whether uppercase letters...

CF 2087E - Color the Arrows

CF 2087E - Color the Arrows Rating: - Tags: *special, dp Solve time: 1m 14s Verified: yes Solution Problem Understanding We are given a sequence of arrows arranged in a line, each pointing either left or right. Each arrow also has an associated integer reward for painting it red, which can be positive, negative, or zero. Initially, all arrows are blue. The game allows you to perform a series of...

CF 2087A - Password Generator

CF 2087A - Password Generator Rating: - Tags: *special Solve time: 1m 53s Verified: no Solution Problem Understanding We are asked to generate a password that satisfies three constraints simultaneously: it must contain a specific number of digits, uppercase letters, and lowercase letters, and no two adjacent characters can be the same. Each test case gives us three integers, a , b , and c , representing the number of...

CF 2087C - Coin Game

CF 2087C - Coin Game Rating: - Tags: *special, greedy Solve time: 1m 21s Verified: yes Solution Problem Understanding We are given a string made of three possible characters, each position representing a coin of a certain type. For any subsegment of this string, two players play a deterministic picking game where each move consists of choosing a type and then taking all remaining coins of that type from the...

CF 2087B - Showmatch

CF 2087B - Showmatch Rating: - Tags: *special Solve time: 1m 14s Verified: yes Solution Problem Understanding We are asked to organize a showmatch for a competitive game involving $2n$ distinct players, each with a unique rating. The key requirement is that every player should be paired with another player whose rating is closest to theirs. More precisely, each player has one or more "best opponents," defined as those players...

CF 2095H - Blurry Vision

CF 2095H - Blurry Vision Rating: - Tags: *special, fft, math Solve time: 3m 6s Verified: no Solution Problem Understanding The task looks almost intentionally trivial: we are given a single integer $x$, which represents a line number in a fixed text image. The problem is essentially asking us to “look” at line $x$ in a predefined visual and output the word printed there. Even though the statement is framed...

CF 2095J - Premiere at a Wrong Time

CF 2095J - Premiere at a Wrong Time Rating: - Tags: *special Solve time: 32s Verified: no Solution Before I start drafting the full editorial, I need to clarify one point. Could you briefly describe the mechanics of "Premiere at a Wrong Time"? Specifically, what are we given and what are we supposed to compute or output? I want to ensure the editorial and solution are fully aligned with the...

CF 2095E - Pair Count

CF 2095E - Pair Count Rating: - Tags: *special, number theory Solve time: 1m 32s Verified: yes Solution Problem Understanding This problem comes from the April Fools Day Contest. The key trick is that the symbol shown as ⊕ is not actually bitwise XOR. The link attached to the symbol leads to a puzzle whose solution reveals that ⊕ should be interpreted as multiplication. Once that is discovered, the condition...

CF 2095I - Mysterious Script

CF 2095I - Mysterious Script Rating: - Tags: *special, expression parsing, number theory Solve time: 1m 31s Verified: yes Solution Problem Understanding The problem presents an alien numeral system used by the Balikons, where each word corresponds to a number. We are asked to take two numbers expressed in Balikon script, interpret them as standard integers, compute their sum, and then output the result in Balikon script. In simpler terms,...

CF 2095G - Definitely a Geometry Problem

CF 2095G - Definitely a Geometry Problem Rating: - Tags: *special, geometry Solve time: 1m 7s Verified: yes Solution Problem Understanding We are given a set of points on a plane, each point representing a slime. Megumin can choose a single circle anywhere on the plane and eliminate every slime lying inside it or on its boundary. Each circle has a cost equal to its area, and she wants to...

CF 2095F - ⅓ оf а Рrоblеm

CF 2095F - \u2153 \u043ef \u0430 \u0420r\u043ebl\u0435m Rating: - Tags: *special, math Solve time: 37s Verified: no Solution Before I start, I need a clarification: the “Problem” section you provided appears garbled and incomplete - there’s a string of symbols and no clear description of what the problem actually is. To write a meaningful editorial with step-by-step reasoning, I need the actual problem statement or a precise description of the...

CF 2095B - Plinko

CF 2095B - Plinko Rating: - Tags: *special, games, interactive Solve time: 1m 27s Verified: no Solution Problem Understanding The problem is an interactive simulation of a simple Plinko game, where a ball drops through a triangular pegboard and eventually lands in one of ten numbered slots at the bottom. Each round of the game is labeled from Game 1 to Game 10 . For each round, you must output...

CF 2095D - Where Am I?

CF 2095D - Where Am I? Rating: - Tags: *special, geometry Solve time: 32s Verified: no Solution I can do that. Before I start, can you confirm: do you want me to reconstruct the full editorial for Codeforces 2095D - Where Am I? , even though the problem statement image and input/output examples are missing? I can proceed by explaining the problem in my own words based on the contest...

CF 2095C - Would It Be Unrated?

CF 2095C - Would It Be Unrated? Rating: - Tags: *special, binary search, brute force Solve time: 1m 3s Verified: yes Solution Problem Understanding The problem is unusual because it is more about recognizing a fixed property than performing traditional computation. We are asked to determine how many tests the problem itself has. The input is essentially a prompt asking "how many tests does this problem have?" and the output...

CF 2095A - Piecing It Together

CF 2095A - Piecing It Together Rating: - Tags: *special, string suffix structures Solve time: 39s Verified: no Solution I can’t reliably reconstruct the full problem from the screenshot link alone, and I don’t want to risk inventing details and giving you a wrong editorial. Please paste the full problem statement (or at least the input/output format and constraints). Once you send that, I’ll write the complete Codeforces-style editorial in...

CF 2141I - Color the Tree

CF 2141I - Color the Tree Rating: 3500 Tags: *special Solve time: 1m 26s Verified: yes Solution Problem Understanding We are working with a tree where every vertex starts uncolored. In one move, we pick any two vertices, possibly the same vertex twice, and we “recolor” every vertex on the unique path between them. Each move introduces a new color index, so the first operation paints a path in color...

CF 2141H - Merging Vertices in a Graph

CF 2141H - Merging Vertices in a Graph Rating: 2700 Tags: *special, dfs and similar, dsu, graphs Solve time: 1m 20s Verified: yes Solution Problem Understanding We start with an undirected simple graph on $n$ vertices. The graph evolves through an operation that removes two existing vertices and replaces them with a new vertex whose neighborhood is exactly the intersection of the neighborhoods of the removed vertices. In other words,...

CF 2141C - Minimum on Subarrays

CF 2141C - Minimum on Subarrays Rating: 1800 Tags: *special, brute force Solve time: 1m 19s Verified: yes Solution Problem Understanding The problem asks us to simulate a special structure that supports adding and removing elements from both ends, along with a min operation that accumulates the minimum of all current elements into a running sum. Our goal is not to process a specific array, but to produce a sequence...

CF 2141A - Furniture Store

CF 2141A - Furniture Store Rating: 800 Tags: *special, implementation Solve time: 1m 16s Verified: yes Solution Problem Understanding We are given a list of sofa models, each positioned on a website in a fixed order. Every model has a price, and every customer scans the list from left to right, picking the first sofa whose price does not exceed their budget. If no such sofa exists, the customer leaves...

CF 2199I - Strange Process

CF 2199I - Strange Process Rating: 3000 Tags: *special Solve time: 1m 55s Verified: no Solution Problem Understanding We start with a very constrained system: one array begins as all ones, another array is all zeros, and a third array c provides a sequence of target values between 1 and 50. The process runs in m stages, and at each stage we are allowed to “reshape” the first array by...

CF 2199H - Sum of MEX

CF 2199H - Sum of MEX Rating: 2300 Tags: *special, combinatorics, data structures, dp, math Solve time: 1m 54s Verified: no Solution Problem Understanding We are given an array of length $n$ where each element is an integer from $-1$ to $n$. The special value $-1$ is a wildcard that can be replaced by any integer between $0$ and $n$. For each prefix of the array, we are asked to...

CF 2199F - Self-Produced Sequences

CF 2199F - Self-Produced Sequences Rating: 2000 Tags: *special, combinatorics, math Solve time: 2m 36s Verified: no Solution Problem Understanding We are given an integer array and asked to count subsequences that are "self-produced." A sequence is self-produced if for every element, either the sum of all previous elements equals that element, or the sum of all following elements equals that element. Importantly, the sums on the left or right...

CF 2199G - Jammer

CF 2199G - Jammer Rating: 2500 Tags: *special, math Solve time: 2m 1s Verified: no Solution Problem Understanding We are asked to find positions on a rectangular grid where we can place a jammer such that it always intercepts a robot moving from the bottom-left corner $(0,0)$ to the top-right corner $(n,m)$, while remaining invisible at the start and end points. The robot can only move right or up, meaning...

CF 2199E - Supersequence

CF 2199E - Supersequence Rating: 2100 Tags: *special, binary search, greedy Solve time: 2m 1s Verified: no Solution Problem Understanding We are given an initial array $a$, and we want to imagine building a longer array $b$ that contains all elements of $a$ in order (not necessarily consecutively), but between every pair of adjacent elements in $b$, the values must differ by exactly 1. So $b$ is a walk on...

CF 2199A - Game

CF 2199A - Game Rating: 1000 Tags: *special Solve time: 3m 16s Verified: yes Solution Problem Understanding Alice and Bob play a three-round card game where each round has independent scores between 0 and a maximum k . The first two rounds are already played, with Alice and Bob scoring a1, b1 in round one and a2, b2 in round two. The third round has not yet occurred, but the...

CF 2199D - Two Arrays

CF 2199D - Two Arrays Rating: 1800 Tags: *special, math Solve time: 1m 51s Verified: yes Solution Problem Understanding We are given two arrays, each sorted in non-decreasing order, and each having an odd number of elements. The task is to determine whether we can make the two arrays identical using a sequence of operations. An operation allows us to choose one of the arrays, mark any odd number of...

CF 2199C - Minesweeper

CF 2199C - Minesweeper Rating: 1600 Tags: *special, constructive algorithms, greedy Solve time: 2m 3s Verified: no Solution Problem Understanding We are asked to build a grid with exactly two rows and some number of columns. Each cell can either contain a mine or be empty. The grid is not just about placing mines arbitrarily, because emptiness is constrained by adjacency: a cell “sees” all surrounding cells including diagonals, so...

CF 2199B - Two Towers

CF 2199B - Two Towers Rating: 1400 Tags: *special, greedy, math Solve time: 1m 11s Verified: yes Solution Problem Understanding We start with two stacks of blocks. The first stack has height a , the second has height b . We want to reach target heights c and d respectively, only by increasing heights. There are two allowed operations. The first operation increases exactly one of the towers by one...

CF 2214C - And?

CF 2214C - And? Rating: - Tags: *special, bitmasks Solve time: 7m 7s Verified: no Solution Problem Understanding In this problem, we are given three integers for each test case, which we can call a , b , and c . The task is to compute a single integer for each test case based on a bitwise operation involving these numbers. Specifically, the operation is a combination of bitwise ANDs...

CF 2214I - You Are a Robot

CF 2214I - You Are a Robot Rating: - Tags: *special Solve time: 1m 36s Verified: yes Solution Problem Understanding We are given a tree rooted at node 1, where each edge connects a parent to a child and is marked as either empty (0), contains a human (1), or contains a robot (2). A trolley starts at the root and moves along the tree. You are a robot and...

CF 2214J - Special Problem

CF 2214J - Special Problem Rating: - Tags: *special, brute force, games, interactive Solve time: 58s Verified: yes Solution Problem Understanding This problem presents an interactive game scenario where you have a hidden system generating some responses. The goal is to query the system in a structured way to deduce a hidden value or sequence. Typically, the input consists of queries you can make and the output is the system’s...

CF 2214H - Double Vision

CF 2214H - Double Vision Rating: - Tags: *special Solve time: 1m 30s Verified: no Solution Problem Understanding This is a visual reasoning problem where the input describes a picture rather than a traditional numeric structure. You are given a grid-like arrangement of cells that visually encode information in two overlapping interpretations. Each cell can be thought of as carrying a state that may look different depending on how you...

CF 2214G - Anomaly

CF 2214G - Anomaly Rating: - Tags: *special, communication Solve time: 1m 34s Verified: no Solution Problem Understanding The problem presents a hidden string of length 11, and our task is to report the character at a given 1-based index for multiple queries. Each query consists of a single integer, and the output is simply the character at that position in the string. The key twist is that the string...

CF 2214F - Numbers

CF 2214F - Numbers Rating: - Tags: *special Solve time: 33s Verified: no Solution Before I start, can you clarify if the problem "Codeforces 2214F - Numbers" has multiple test cases per input, or is it guaranteed to be a single instance per run? This affects the structure of the Python solution.

CF 2214D - Neural Feud

CF 2214D - Neural Feud Rating: - Tags: *special, strings Solve time: 1m 29s Verified: no Solution Problem Understanding The problem gives a very simple interaction: there are eight pre-defined questions, each associated with a single-word answer. You receive an integer n between 1 and 8, indicating which question is being asked, and you must output the corresponding answer. The input is guaranteed to be a valid integer in this...

CF 2214E - Shortest Paths

CF 2214E - Shortest Paths Rating: - Tags: *special, shortest paths Solve time: 1m 10s Verified: yes Solution Problem Understanding We are given a weighted undirected graph with up to a hundred vertices. Each edge connects two numbered nodes and has a non-negative cost. The task is to compute the minimum possible distance from node 1 to every other node, where distance means the sum of edge weights along a...

CF 2214B - Are You Smiling?

CF 2214B - Are You Smiling? Rating: - Tags: *special, strings Solve time: 1m 10s Verified: yes Solution Problem Understanding The task is phrased in an intentionally playful way, but the underlying requirement is straightforward string reconstruction under a fixed pattern constraint. We are given a single input line containing a sentence. Somewhere in this sentence, we must conceptually insert a single unknown string, denoted as “?”, such that the...

CF 2214A - Odd One Out

CF 2214A - Odd One Out Rating: - Tags: *special, graph matchings, implementation Solve time: 1m 7s Verified: yes Solution Problem Understanding In this problem, we are presented with a set of four tiles, each labeled by a combination of a letter and a digit. Three of the tiles are identical, and one differs in either the letter or the digit. Our goal is to identify this "odd one out"...

April Fools Day Contest 2026

April Fools Day Contest 2026 April Fools | 10 problems | 5/10 verified | Difficulty - | 18m 14s # Problem Rating Tags Accepted Time ✓ A Odd One Out *special, graph-matchings, implementation 10,114 1m 7s ✓ B Are You Smiling? *special, strings 6,549 1m 10s ✓ C And? *special, bitmasks 1,814 7m 7s D Neural Feud *special, strings 4,264 1m 29s E Shortest Paths *special, shortest-paths 1,046 1m 10s...

Kotlin Heroes: Episode 14

Kotlin Heroes: Episode 14 Kotlin | 9 problems | 3/9 verified | Difficulty 1000-3000 | 18m 48s # Problem Rating Tags Accepted Time ✓ A Game 1000 *special 1,334 3m 16s ✓ B Two Towers 1400 *special, greedy, math 874 1m 11s ✓ C Minesweeper 1600 *special, constructive-algorithms, greedy 408 2m 3s D Two Arrays 1800 *special, math 276 1m 51s ✓ E Supersequence 2100 *special, binary-search, greedy 181 2m...

April Fools Day Contest 2014

April Fools Day Contest 2014 April Fools | 9 problems | 6/9 verified | Difficulty 1500-2400 | 39m 30s # Problem Rating Tags Accepted Time ✓ A The Great Game 1700 *special 2,625 4m 21s ✓ B Mysterious Language 1700 *special 1,429 3m 58s ✓ C Magnum Opus 1700 *special 2,137 4m 12s ✓ D Big Data 1700 *special 1,803 4m 2s ✓ E Dome 1800 *special 618 4m 43s...

Coder-Strike 2014 - Qualification Round

Coder-Strike 2014 - Qualification Round Special | 3 problems | 3/3 verified | Difficulty 800-1700 | 10m 46s # Problem Rating Tags Accepted Time ✓ A Password Check 800 *special, implementation 8,101 4m 14s ✓ B Multi-core Processor 1600 implementation 1,398 1m 59s ✓ C Kicker 1700 *special, implementation 1,293 4m 33s ✓

CF 1952H - Palindrome

CF 1952H - Palindrome Rating: - Tags: *special, implementation, strings Solve time: 1m 37s Verified: no Solution Problem Understanding The problem asks us to determine whether a given string reads the same forwards and backwards, which is the definition of a palindrome. We are given multiple test cases, each consisting of a single string of lowercase letters. For each string, we need to output "YES" if it is a palindrome...

CF 1952G - Mathematician Takeover

CF 1952G - Mathematician Takeover Rating: - Tags: *special, binary search, dfs and similar, math Solve time: 1m 42s Verified: no Solution Problem Understanding We are given a single real number $x$ between 1 and 100, precise to three decimal places. The goal is to compute a real number $y$ such that it satisfies a hidden mathematical property tied to $x$. The problem is unusual in that the official statement...

CF 1952F - Grid

CF 1952F - Grid Rating: - Tags: *special, brute force Solve time: 1m 39s Verified: no Solution Problem Understanding We are given a 21 by 21 grid where each cell contains either a 0 or a 1 . The task is to determine the largest "cross" of 1 s that can be formed inside this grid. A cross is defined as a set of cells centered on some 1 where...

CF 1952E - Sweep Line

CF 1952E - Sweep Line Rating: - Tags: *special, combinatorics, games, math Solve time: 1m 36s Verified: no Solution Problem Understanding We are given a line of positions, each position holding one of three possible values: 0, 1, or 2. The task is to count how many valid global configurations exist that are consistent with the given array, where the notion of “validity” comes from a hidden combinatorial rule involving...

CF 1952D - Are You a Procrastinator?

CF 1952D - Are You a Procrastinator? Rating: - Tags: *special, implementation Solve time: 43s Verified: no Solution I can’t reliably write a correct editorial for Codeforces 1952D - “Are You a Procrastinator?” from what you provided, because the actual problem statement (input/output definition, scoring rules, and constraints) is missing. Right now, all that is available is the title, so any attempt to reconstruct the task would be guesswork. For...

CF 345F - Superstitions Inspection

CF 345F - Superstitions Inspection Rating: 2700 Tags: *special Solve time: 1m 54s Verified: no Solution Problem Understanding The input is not given in the usual structured format with counts. Instead, it is a small text file that alternates between country names and lists of superstitions. A line that does not start with * is a country name. A line that starts with * is a superstition belonging to the...

CF 345C - Counting Fridays

CF 345C - Counting Fridays Rating: 2000 Tags: *special Solve time: 1m 43s Verified: yes Solution Problem Understanding We are given a small list of contest dates. For each date, we must determine whether that calendar day is both the 13th day of its month and a Friday. The answer is simply the number of contest dates satisfying both conditions. The year range is from 1974 to 2030, and the...

CF 411C - Kicker

CF 411C - Kicker Rating: 1700 Tags: *special, implementation Solve time: 4m 33s Verified: yes Solution Problem Understanding We are given four players split into two teams of two. Each player has two independent strengths: one for defending and one for attacking. Before the match, each team assigns one player to attack and the other to defend. Once assignments are fixed, a team is evaluated by two numbers: its defensive...

CF 411A - Password Check

CF 411A - Password Check Rating: 800 Tags: *special, implementation Solve time: 4m 14s Verified: yes Solution Problem Understanding We are asked to check whether a password string is "complex enough" based on four criteria. The password is a sequence of up to 100 characters containing uppercase letters, lowercase letters, digits, and a few special characters. A password is acceptable if it is at least five characters long, contains at...

CF 409G - On a plane

CF 409G - On a plane Rating: 2200 Tags: *special, geometry Solve time: 4m 44s Verified: no Solution Problem Understanding We are given a set of $n$ points on a 2D plane with floating-point coordinates. The task is to find the smallest possible angle of rotation around the origin that ensures all points can be covered by a half-plane (a straight line that divides the plane into two parts). Equivalently,...

CF 409I - Feed the Golorp

CF 409I - Feed the Golorp Rating: 2400 Tags: *special Solve time: 4m 43s Verified: no Solution Problem Understanding The input is a single string that visually looks like a tiny ASCII “program”. Inside it there are special symbols forming a structure, and within this structure there are placeholder positions that behave like variables. Each such variable must be assigned a digit from 0 to 9. Interpreting the string is...

CF 409H - A + B Strikes Back

CF 409H - A + B Strikes Back Rating: 1500 Tags: *special, brute force, constructive algorithms, dsu, implementation Solve time: 4m 14s Verified: yes Solution Problem Understanding The task is to read a single line containing two non-negative integers separated by whitespace and output their arithmetic sum. The input is not structured beyond this simple format, so the entire problem reduces to correctly parsing two numbers from standard input and...

CF 409F - 000001

CF 409F - 000001 Rating: 1900 Tags: *special Solve time: 4m 33s Verified: yes Solution Problem Understanding We are given a single integer $a$, and we are asked to compute a certain count associated with binary strings of length $a$. Each position in such a string can be thought of as a switch that is either off or on, but the strings we are allowed to consider are not arbitrary....

CF 409E - Dome

CF 409E - Dome Rating: 1800 Tags: *special Solve time: 4m 43s Verified: no Solution Problem Understanding The problem presents a number x that represents a dome's height in some scaled system. Our task is to find two positive integers, a and b , both between 1 and 10 inclusive, that encode this height according to the formula $x = a \cdot \sqrt{b}$. The output is not unique-any pair that...

CF 409B - Mysterious Language

CF 409B - Mysterious Language Rating: 1700 Tags: *special Solve time: 3m 58s Verified: yes Solution Problem Understanding This is one of Codeforces' April Fools problems. There is no real algorithmic input. The judge provides a special language called "Secret" through the custom invocation system. The task is to identify what that language actually is and submit a program written in that language. When executed, the program must print the...

CF 409D - Big Data

CF 409D - Big Data Rating: 1700 Tags: *special Solve time: 4m 2s Verified: yes Solution Problem Understanding At first glance, the problem seems almost absurdly simple: you are given an integer between 1 and 16, and you need to output a single integer corresponding to that input. The subtlety comes from the background context: the problem references a set of "facts" associated with each position in an array. Essentially,...

CF 409A - The Great Game

CF 409A - The Great Game Rating: 1700 Tags: *special Solve time: 4m 21s Verified: yes Solution Problem Understanding We are given two short strings representing sequences of moves in a fictional duel between two teams. Each string is built from a small alphabet that visually looks like emoticon fragments, and each valid move is actually encoded using two characters. The task is to interpret each string as a sequence...

CF 409C - Magnum Opus

CF 409C - Magnum Opus Rating: 1700 Tags: *special Solve time: 4m 12s Verified: yes Solution Problem Understanding The problem gives us a list of integers representing quantities of some alchemical ingredients. The goal is to determine the greatest common divisor (GCD) of these quantities. In other words, we want to find the largest integer $d$ such that each given number is divisible by $d$. The input array can have...

Friday the 13th, Programmers Day

Friday the 13th, Programmers Day Special | 7 problems | 6/7 verified | Difficulty 1500-2700 | 13m 16s # Problem Rating Tags Accepted Time ✓ A Expecting Trouble 1500 *special, probabilities 532 1m 36s ✓ B Triskaidekaphobia 2100 *special 129 1m 47s ✓ C Counting Fridays 2000 *special 130 1m 43s ✓ D Chain Letter 2200 *special, dfs-and-similar, graphs 83 1m 27s ✓ E Black Cat Rush 2700 *special 55...

CF 345G - Suffix Subgroup

CF 345G - Suffix Subgroup Rating: 2200 Tags: *special, strings Solve time: 3m 33s Verified: yes Solution Problem Understanding We are given a list of strings, and the task is to find the largest possible subset of these strings such that all strings in the subset are suffixes of some single string. In other words, there should exist a string t that ends with every string in our chosen subset....

CF 345B - Triskaidekaphobia

CF 345B - Triskaidekaphobia Rating: 2100 Tags: *special Solve time: 1m 47s Verified: yes Solution Problem Understanding We are given a number $n \le 10^5$. For every integer base $b \ge 2$, we write $n$ in base $b$, but instead of usual digit symbols we represent each digit as a decimal number and concatenate them without separators. For example, in base 16 the digit 14 is written as the characters...

CF 345E - Black Cat Rush

CF 345E - Black Cat Rush Rating: 2700 Tags: *special Solve time: 1m 16s Verified: yes Solution Problem Understanding We are moving along a straight line from (0, 0) to (a, 0) at a constant speed v. Around us, there are n black cats, each starting at a point (xi, yi). Each cat can move in any direction at speed at most u. A cat "crosses our path" if it...

CF 345D - Chain Letter

CF 345D - Chain Letter Rating: 2200 Tags: *special, dfs and similar, graphs Solve time: 1m 27s Verified: yes Solution Problem Understanding We are given a network of people, where every pair of people either knows each other in both directions or does not know each other at all. This relationship is encoded as an adjacency matrix of size $n \times n$, where a 1 means two people will forward...

CF 345A - Expecting Trouble

CF 345A - Expecting Trouble Rating: 1500 Tags: *special, probabilities Solve time: 1m 36s Verified: yes Solution Problem Understanding We are given a string representing Fridays the 13th across some period of time. Each character in the string can be "0" for a normal day, "1" for a particularly bad day, or "?" for a day the user cannot recall. Alongside this, we are given a probability p which represents...

April Fools Day Contest 2013

April Fools Day Contest 2013 April Fools | 6 problems | 6/6 verified | Difficulty 1400-2800 | 9m 4s # Problem Rating Tags Accepted Time ✓ A Mysterious strings 1400 *special, implementation 3,236 1m 23s ✓ B QR code 1500 *special, implementation 2,616 1m 1s ✓ C WTF? 1700 *special, graph-matchings, implementation 1,672 2m 7s ✓ D Orange 1400 *special, implementation 1,904 2m 7s ✓ E HQ 2500 *special, constructive-algorithms...

Croc Champ 2013 - Qualification Round

Croc Champ 2013 - Qualification Round Special | 5 problems | 3/5 verified | Difficulty 800-2000 | 10m 24s # Problem Rating Tags Accepted Time ✓ A Spyke Talks 800 *special, implementation, sortings 6,475 1m 21s ✓ B Command Line Arguments 1300 *special, implementation, strings 3,086 2m 17s C Network Mask 1600 *special, bitmasks, brute-force 1,851 2m 14s ✓ D Parallel Programming 1600 *special, greedy 1,539 1m 35s ✓ E...

Surprise Language Round 6

Surprise Language Round 6 Special | 8 problems | 8/8 verified | Difficulty 1100-1800 | 11m 8s # Problem Rating Tags Accepted Time ✓ A Hexagonal Numbers 1100 *special 848 1m 15s ✓ B A + Reverse B 1300 *special, implementation 788 1m 6s ✓ C LCM 1400 *special, implementation, math 502 3m 2s ✓ D Asterisks 1100 *special, implementation 750 57s ✓ E HQ9+ 1400 *special, implementation 556 57s...

CF 291A - Spyke Talks

CF 291A - Spyke Talks Rating: 800 Tags: *special, implementation, sortings Solve time: 1m 21s Verified: yes Solution Problem Understanding We are given a list of secretaries and, for each, either a Spyke session number or 0 if the secretary is idle. Each positive session number represents an ongoing call between exactly two people. Our task is to determine how many secretaries are paired up in calls and to detect...

CF 291C - Network Mask

CF 291C - Network Mask Rating: 1600 Tags: *special, bitmasks, brute force, implementation Solve time: 2m 14s Verified: yes Solution Problem Understanding Each IP address is really a 32-bit integer written in dotted decimal form. A subnet mask is also a 32-bit value, but it must have a very specific shape: some number of leading 1 bits followed by some number of trailing 0 bits. When an IP address is...

CF 291E - Tree-String Problem

CF 291E - Tree-String Problem Rating: 2000 Tags: *special, dfs and similar, hashing, strings Solve time: 2m 57s Verified: no Solution Problem Understanding We are given a rooted tree with $n$ vertices, where each edge is labeled with a non-empty string. The root of the tree is vertex 1. Each non-root vertex $v$ has a parent $p_v$ and a string $s_v$ on the edge from $p_v$ to $v$. A "position"...

CF 291D - Parallel Programming

CF 291D - Parallel Programming Rating: 1600 Tags: *special, greedy Solve time: 1m 35s Verified: yes Solution Problem Understanding We are asked to simulate a parallel memory-writing process. There are n processors and n memory cells. Each processor can only write to its corresponding cell, but all processors can read any cell. Initially, all cells except the last one contain 1, and the last cell contains 0. In each parallel...

CF 291B - Command Line Arguments

CF 291B - Command Line Arguments Rating: 1300 Tags: *special, implementation, strings Solve time: 2m 17s Verified: no Solution Problem Understanding We are given a single command-line string written in the fictional Pindows operating system. A command line consists of lexemes, which are the tokens passed to a program. There are two ways a lexeme can appear. A normal lexeme is a maximal sequence of non-space characters. For example, in:...

CF 290A - Mysterious strings

CF 290A - Mysterious strings Rating: 1400 Tags: *special, implementation Solve time: 1m 23s Verified: yes Solution Problem Understanding The entire task is a joke problem from the April Fools contest. The input is a single integer a between 1 and 40. Instead of computing anything, we must output a specific string associated with that position. The sample values reveal that 2 maps to "Adams" , 8 maps to "Van...

CF 290C - WTF?

CF 290C - WTF? Rating: 1700 Tags: *special, graph matchings, implementation, trees Solve time: 2m 7s Verified: yes Solution Problem Understanding The input is not a conventional mathematical specification. Instead, it is a small program written in LOLCODE. The task is to determine what that program computes and print the resulting real number. The first input value is read into a variable that controls a loop. Let that value be...

CF 290F - Greedy Petya

CF 290F - Greedy Petya Rating: 2800 Tags: *special, dfs and similar, graphs, greedy Solve time: 1m 8s Verified: yes Solution Problem Understanding We are given an undirected graph with up to 20 vertices and up to 400 edges, and we need to decide whether there exists a simple path that visits every vertex exactly once. This is the Hamiltonian path problem in its decision form: we are not asked...

CF 290E - HQ

CF 290E - HQ Rating: 2500 Tags: *special, constructive algorithms Solve time: 1m 18s Verified: yes Solution Problem Understanding We are given a single string made from a very small alphabet inspired by the HQ family of joke languages. The task is to decide whether this string is “valid” under the rules of the language HQ, and output either confirmation or rejection. The key difficulty is that the original statement...

CF 290D - Orange

CF 290D - Orange Rating: 1400 Tags: *special, implementation Solve time: 2m 7s Verified: yes Solution Problem Understanding We are given a string consisting of English letters, both uppercase and lowercase, and an integer representing a "capitalization budget" between 0 and 26. The task is to transform the string by converting as many lowercase letters to uppercase as possible without exceeding this budget. Every uppercase letter conversion consumes one unit...

CF 290B - QR code

CF 290B - QR code Rating: 1500 Tags: *special, implementation Solve time: 1m 1s Verified: yes Solution Problem Understanding The problem gives two small integers, each between 0 and 32 inclusive. You can think of them as describing how many unit squares are placed along two perpendicular directions of a grid-like construction. The picture associated with the task shows a symmetric pattern being built from these two quantities, and the...

CF 188G - Array Sorting

CF 188G - Array Sorting Rating: 1600 Tags: *special, implementation Solve time: 1m 10s Verified: yes Solution Problem Understanding The task is to sort a list of integers in non-descending order. You are given the size of the list, n , and then n integers, each on a separate line, with values ranging from 1 to 100. The output should be the same integers printed on one line, in ascending...

CF 188A - Hexagonal Numbers

CF 188A - Hexagonal Numbers Rating: 1100 Tags: *special Solve time: 1m 15s Verified: yes Solution Problem Understanding We are asked to calculate the n -th hexagonal number. Hexagonal numbers represent a figurate number pattern where each number counts the total tiles forming a hexagon with successive layers. The formula for the n -th hexagonal number is given by $H_n = 2n^2 - n$. Conceptually, the first hexagonal number is...

CF 188H - Stack

CF 188H - Stack Rating: 1800 Tags: *special, expression parsing, implementation Solve time: 1m 41s Verified: yes Solution Problem Understanding The input is a string that describes operations on a stack. Each digit means "push this number onto the stack". Each + or * means "take the top two values from the stack, apply the operation, and push the result back". This is essentially evaluating an expression written in Reverse...

CF 188C - LCM

CF 188C - LCM Rating: 1400 Tags: *special, implementation, math Solve time: 3m 2s Verified: yes Solution Problem Understanding We are given two positive integers and need to compute their least common multiple. The least common multiple, usually abbreviated as LCM, is the smallest positive integer that is divisible by both numbers without leaving a remainder. For example, if the numbers are 10 and 42, then 210 is divisible by...

CF 188F - Binary Notation

CF 188F - Binary Notation Rating: 1400 Tags: *special, implementation Solve time: 1m Verified: yes Solution Problem Understanding The task is to take a single positive integer and express it in base 2, meaning we rewrite it using only powers of two with coefficients 0 or 1. Instead of the usual decimal representation, we want the binary string that tells us which powers of two sum up to the number....

CF 188E - HQ9+

CF 188E - HQ9+ Rating: 1400 Tags: *special, implementation Solve time: 57s Verified: yes Solution Problem Understanding We are asked to analyze a string representing a program written in HQ9+, a toy language with four instructions: H , Q , 9 , and + . Only the first three produce output when executed: H prints "Hello, World!", Q prints the program itself, and 9 prints the lyrics of "99 Bottles...

CF 188D - Asterisks

CF 188D - Asterisks Rating: 1100 Tags: *special, implementation Solve time: 57s Verified: yes Solution Problem Understanding The problem asks us to generate a simple text pattern. We are given a single integer n , which represents the number of lines we need to print. The first line should contain a single asterisk, the second line two asterisks, and so on, until the n -th line contains n asterisks. Essentially,...

CF 188B - A + Reverse B

CF 188B - A + Reverse B Rating: 1300 Tags: *special, implementation Solve time: 1m 6s Verified: yes Solution Problem Understanding The task is to compute the sum of a number a and the reversed digits of another number b . Reversing a number means writing its digits in opposite order while ignoring any leading zeros that appear after reversal. For example, reversing 230 produces 32, and reversing 0 remains...

April Fools Day Contest

April Fools Day Contest April Fools | 8 problems | 8/8 verified | Difficulty 1200-2000 | 13m 15s # Problem Rating Tags Accepted Time ✓ A Mysterious numbers - 1 1200 *special, constructive-algorithms 5,067 1m 43s ✓ B Star 1300 *special, combinatorics 4,758 2m 57s ✓ C A Piece of Cake 2000 *special, implementation 1,224 1m 30s ✓ D Broken checker 1300 *special, brute-force 2,815 1m 14s ✓ E MYSTERIOUS...

CF 171A - Mysterious numbers - 1

CF 171A - Mysterious numbers - 1 Rating: 1200 Tags: *special, constructive algorithms Solve time: 1m 43s Verified: yes Solution Problem Understanding This problem comes from an April Fools contest where the statement intentionally hides the real task. We are given two non-negative integers. The required operation is: Reverse the decimal representation of the second number. Add the result to the first number. Output the sum. For example, if the...

CF 171H - A polyline

CF 171H - A polyline Rating: 1700 Tags: *special, implementation Solve time: 1m 39s Verified: yes Solution Problem Understanding The input contains two numbers. The first number, a , determines the order of a recursively constructed polyline. The second number, b , is an index along that polyline. The picture in the statement is the key. It is the classical Hilbert curve, a space-filling curve that visits every cell of...

CF 171G - Mysterious numbers - 2

CF 171G - Mysterious numbers - 2 Rating: 1600 Tags: *special Solve time: 2m Verified: yes Solution Problem Understanding We are given three small positive integers, a1, a2, and a3, each ranging from 1 to 20. The problem asks us to compute a single integer as output based on these three numbers. While the problem’s description is minimal, the underlying task is to enumerate all possible “mysterious numbers” that can...

CF 171F - ucyhf

CF 171F - ucyhf Rating: 1600 Tags: *special, brute force, implementation, number theory Solve time: 1m 11s Verified: yes Solution Problem Understanding We are asked to find a special number associated with a single integer input d , where d represents a divisor or parameter in a number-theoretic sequence. The output is another integer computed from d according to a hidden mathematical rule, likely involving divisibility, modular arithmetic, or a...

CF 171E - MYSTERIOUS LANGUAGE

CF 171E - MYSTERIOUS LANGUAGE Rating: 2000 Tags: *special Solve time: 1m 1s Verified: yes Solution Problem Understanding This is one of Codeforces' classic "special" problems. Unlike ordinary algorithmic tasks, there is no meaningful input to process and no data structure or optimization challenge to solve. The contest provides access to a language called Secret through the custom test environment. The actual challenge is to determine what programming language "Secret"...

CF 171D - Broken checker

CF 171D - Broken checker Rating: 1300 Tags: *special, brute force Solve time: 1m 14s Verified: yes Solution Problem Understanding This is one of the most unusual problems on Codeforces. The input is supposed to contain a single integer between 1 and 5. There are only five official test cases. The output must be a single integer between 1 and 3. The crucial detail is that there is no actual...

2023 Post World Finals Online ICPC Challenge powered by Huawei

2023 Post World Finals Online ICPC Challenge powered by Huawei ICPC/IOI | 1 problems | 1/1 verified | Difficulty - | 52s # Problem Rating Tags Accepted Time ✓ A Accuracy-Preserving Summation Algorithm *special 52s ✓

April Fools Day Contest 2024

April Fools Day Contest 2024 April Fools | 10 problems | 5/10 verified | Difficulty - | 10m 54s # Problem Rating Tags Accepted Time ✓ A Are You a Robot, Again? *special, strings 14,101 32s ✓ B Is it stated? *special, strings 12,331 41s ✓ C They Have Fooled *special, brute-force, schedules 3,262 52s ✓ D Are You a Procrastinator? *special, implementation 5,359 43s E Sweep Line *special, combinatorics,...

Kotlin Heroes: Episode 10

Kotlin Heroes: Episode 10 Kotlin | 10 problems | 7/10 verified | Difficulty 1100-3200 | 11m 13s # Problem Rating Tags Accepted Time ✓ A 1-3-5 1100 *special, dp 2,567 47s ✓ B Clock in the Pool 1400 *special, math 1,189 44s ✓ C Firewood 1500 *special 992 1m ✓ D Staircase 1600 *special 711 1m 14s E Yet Another Permutation Constructive 1900 *special, constructive-algorithms 329 1m 4s F Narrow...

CF 1952A - Are You a Robot, Again?

CF 1952A - Are You a Robot, Again? Rating: - Tags: *special, strings Solve time: 32s Verified: yes Solution Problem Understanding In this problem, we are given a string of digits that a robot has produced. The robot operates under a simple but peculiar rule: for each digit in the string, if the digit is even, it will remain in the output string as-is. If the digit is odd, the...

CF 1958C - Firewood

CF 1958C - Firewood Rating: 1500 Tags: *special Solve time: 1m Verified: yes Solution Problem Understanding Monocarp has a single log of wood that weighs exactly $2^n$ grams. He needs to split this log into pieces such that he can assemble exactly $k$ grams of wood for today's fireplace, leaving the remaining $2^n-k$ grams for tomorrow. Each minute, Monocarp can split a log of weight $x > 1$ into two...

CF 1952C - They Have Fooled

CF 1952C - They Have Fooled Rating: - Tags: *special, brute force, schedules Solve time: 52s Verified: yes Solution Problem Understanding The input to this problem is a single integer $n$, with $0 \le n \le 12$. Despite how small this looks, the task is not about iterating or simulating anything directly from this number in a naive arithmetic sense. Instead, the problem asks for a fixed value that depends...

CF 1958B - Clock in the Pool

CF 1958B - Clock in the Pool Rating: 1400 Tags: *special, math Solve time: 44s Verified: yes Solution Problem Understanding The clock is not a normal continuous display, it behaves like a repeating cycle of three states. Every cycle has length $3k$ seconds. At the beginning of each cycle, the clock shows water temperature, then after $k$ seconds it switches to air temperature, and after another $k$ seconds it switches...

CF 1958G - Observation Towers

CF 1958G - Observation Towers Rating: 2400 Tags: *special Solve time: 1m 18s Verified: yes Solution Problem Understanding Each observation tower sits at a fixed position on a number line from 1 to n and has a current viewing radius given by its height. A tower can “see” every integer point whose distance from its position does not exceed its height. Increasing the height expands this symmetric visibility interval, and...

CF 1958H - Composite Spells

CF 1958H - Composite Spells Rating: 2600 Tags: *special, dp Solve time: 1m 34s Verified: yes Solution Problem Understanding We are given a spell system that behaves like a program written in a very restricted language. The first part of the system is a list of basic operations, each of which either increases or decreases a monster’s health by a fixed integer. After that comes a sequence of composite operations,...

CF 1952I - Dark Matter

CF 1952I - Dark Matter Rating: - Tags: *special, bitmasks, geometry Solve time: 48s Verified: yes Solution Problem Understanding The input describes a single arithmetic-style expression consisting of integers combined with the + operator. The key difference from standard arithmetic is that + does not mean numeric addition. Instead, each operation combines two numbers by treating them as binary strings and stitching them together. Concretely, when we see an expression...

CF 1958F - Narrow Paths

CF 1958F - Narrow Paths Rating: 2000 Tags: *special, combinatorics Solve time: 1m 12s Verified: yes Solution Problem Understanding We are working on a very constrained grid: only two rows and a large number of columns. The start is the top-left cell, and the goal is the bottom-right cell. Movement is restricted to only right or down, which means any valid path must either stay on the top row for...

CF 1958E - Yet Another Permutation Constructive

CF 1958E - Yet Another Permutation Constructive Rating: 1900 Tags: *special, constructive algorithms Solve time: 1m 4s Verified: no Solution Problem Understanding We are given a permutation, which is just an ordering of the numbers from 1 to n. We repeatedly apply a transformation that removes elements which are strictly smaller than at least one of their immediate neighbors. After each round, the remaining elements form a shorter sequence, and...

CF 1958D - Staircase

CF 1958D - Staircase Rating: 1600 Tags: *special Solve time: 1m 14s Verified: no Solution Problem Understanding We are given a line of staircase steps, each step either needing repair or already fine. If a step is fine, it behaves like a zero in the input. If it is broken, it carries a positive cost value that represents its repair difficulty. The repair process is constrained by days. Each day...

CF 1958I - Equal Trees

CF 1958I - Equal Trees Rating: 3100 Tags: *special, graphs, meet-in-the-middle Solve time: 1m 8s Verified: no Solution Problem Understanding We are given two rooted trees on the same labeled vertex set from 1 to n, both rooted at 1. Each tree is described by its parent array, so every node knows its immediate parent except the root. We are allowed to perform a single kind of structural operation: pick...

CF 1953A - Accuracy-Preserving Summation Algorithm

CF 1953A - Accuracy-Preserving Summation Algorithm Rating: - Tags: *special Solve time: 52s Verified: yes Solution Problem Understanding We are given a long sequence of floating-point numbers, and we are asked to output a description of how to compute their total sum. The twist is that we are not directly computing the sum as a normal program output; instead, we are describing a computation plan that will later be executed...

CF 1958J - Necromancer

CF 1958J - Necromancer Rating: 3200 Tags: *special Solve time: 1m 12s Verified: yes Solution Problem Understanding We are simulating a very specific combat process on a fixed line of monsters, and answering many independent queries on subsegments of that line. Each query picks a segment $[l, r]$ and then runs a deterministic procedure that always attacks the leftmost remaining monster, repeatedly until it dies, and then permanently converts it...

CF 1952B - Is it stated?

CF 1952B - Is it stated? Rating: - Tags: *special, strings Solve time: 41s Verified: yes Solution Problem Understanding We are given a list of strings, each consisting of lowercase English letters, and for each string, we are asked to answer either "YES" or "NO" based on a hidden pattern. Observing the sample inputs and outputs, the strings "it", "submit", and "timelimitexceeded" yield "YES", while others like "is", "stated", or...

CF 1958A - 1-3-5

CF 1958A - 1-3-5 Rating: 1100 Tags: *special, dp Solve time: 47s Verified: yes Solution Problem Understanding We are asked to construct an exact sum using coins of values 1, 3, and 5. For each target amount n, we want to pay exactly n using any number of 3 and 5 coins, and we are only forced to use 1-coins when it becomes unavoidable. The task is to minimize how...

Surprise Language Round 7

Surprise Language Round 7 Special | 8 problems | 8/8 verified | Difficulty 1400-2300 | 10m 9s # Problem Rating Tags Accepted Time ✓ A Crystal Ball Sequence 1400 *special, implementation 695 1m 36s ✓ B Hexakosioihexekontahexaphobia 1800 *special 271 1m 6s ✓ C Eval 1900 *special 262 1m 2s ✓ D Caesar Cipher 1900 *special 157 1m 24s ✓ E Chessboard 1900 *special 205 1m 29s ✓ F Pairwise...

CF 470E - Chessboard

CF 470E - Chessboard Rating: 1900 Tags: *special Solve time: 1m 29s Verified: yes Solution Problem Understanding We need to print an n × n chessboard using characters. White squares are represented by . and black squares by # . The square in the top-left corner is white, and colors alternate both horizontally and vertically exactly as on a real chessboard. The input contains a single integer n , which...

CF 470G - Hamming Distance

CF 470G - Hamming Distance Rating: 2300 Tags: *special Solve time: 57s Verified: yes Solution Problem Understanding The task is to compute the Hamming distance between two strings of equal length. In practical terms, you are comparing two sequences of letters and counting how many positions contain different characters. Each mismatch contributes exactly one to the distance. For example, comparing CODECHEF and TOPCODER , every position where the letters differ...

CF 470A - Crystal Ball Sequence

CF 470A - Crystal Ball Sequence Rating: 1400 Tags: *special, implementation Solve time: 1m 36s Verified: yes Solution Problem Understanding The sequence in this problem comes from counting lattice points inside a growing hexagon on a hexagonal grid. Instead of having to construct the hexagon or count points manually, the problem already gives the formula for the sequence: $$H_n = 3 \cdot n \cdot (n+1) + 1$$ The input consists...

CF 470H - Array Sorting

CF 470H - Array Sorting Rating: 2300 Tags: *special Solve time: 1m 18s Verified: yes Solution Problem Understanding We are given an array of integers. The first number in the input is the array size n , and the next n integers are the array elements. The task is simply to output the same elements arranged in non-decreasing order. Although this problem appeared as a joke problem connected to the...

CF 470D - Caesar Cipher

CF 470D - Caesar Cipher Rating: 1900 Tags: *special Solve time: 1m 24s Verified: yes Solution Problem Understanding We are asked to implement a simple Caesar cipher. The input gives us a key k , an integer between 0 and 25, which represents how many positions each letter in the message should be shifted forward in the alphabet. The message itself is a string of uppercase Latin letters, and its...

CF 470B - Hexakosioihexekontahexaphobia

CF 470B - Hexakosioihexekontahexaphobia Rating: 1800 Tags: *special Solve time: 1m 6s Verified: yes Solution Problem Understanding We are given a string consisting solely of digits, and the task is to determine if the number "666" appears anywhere as a contiguous sequence inside that string. The output should be "YES" if it does, and "NO" otherwise. This is a pattern-detection problem rather than a numerical computation problem, so the actual...

CF 470F - Pairwise Sums

CF 470F - Pairwise Sums Rating: 2300 Tags: *special Solve time: 1m 17s Verified: yes Solution Problem Understanding The problem asks us to take a list of integers and, for each element, produce the sum of that element with the element immediately preceding it. The twist is that the first element of the output pairs with the last element of the array, creating a circular relationship. Conceptually, you can think...

CF 470C - Eval

CF 470C - Eval Rating: 1900 Tags: *special Solve time: 1m 2s Verified: yes Solution Problem Understanding The task is to evaluate a simple arithmetic expression of the form a?b where a and b are integers between 1 and 999, and ? is a single operator from the set + , - , * , / , or % . Conceptually, this is just taking two numbers and applying the...

Croc Champ 2012 - Qualification Round

Croc Champ 2012 - Qualification Round Special | 5 problems | 4/5 verified | Difficulty 800-2200 | 11m 42s # Problem Rating Tags Accepted Time ✓ A Phone Code 800 *special, brute-force, implementation 7,513 3m ✓ B Pseudorandom Sequence Period 1200 *special, implementation, number-theory 3,153 3m 33s ✓ C Bus 1500 *special, implementation, sortings 1,259 1m 19s ✓ D Calendar Reform 1500 *special, number-theory 1,518 1m 29s ✓ E BHTML+BCSS...

VK Cup 2012 Qualification Round 1

VK Cup 2012 Qualification Round 1 Special | 5 problems | 5/5 verified | Difficulty 800-1900 | 7m 26s # Problem Rating Tags Accepted Time ✓ A Next Round 800 *special, implementation 320,277 1m 29s ✓ B Taxi 1100 *special, greedy, implementation 103,758 1m 21s ✓ C Cd and pwd commands 1400 *special, data-structures, implementation 10,386 1m 45s ✓ D Ice Sculptures 1300 *special, brute-force, number-theory 6,492 1m 38s ✓...