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tamnd's digital brain — notes, problems, research

41641 notes

CF 103914B - Puzzle: Patrick's Parabox

We are given a grid-based puzzle that behaves like a modified Sokoban system with two special entities: a player and a box. Both start on distinct floor cells, and each has a designated target cell.

codeforcescompetitive-programming
CF 103914C - Puzzle: Hearthstone

We are building a sequence of operations that simulate a system with hidden “secret types” from 1 to n. At any moment there is a set of secrets currently present in a zone. However, the crucial complication is that we do not actually know which secret each add refers to.

codeforcescompetitive-programming
CF 103920F - Bit Paths

I don't have enough information to write a correct editorial. The prompt only provides the problem identifier, Codeforces 103920F - Bit Paths, but the Problem Statement, Input, and Output sections are empty.

codeforcescompetitive-programming
CF 103920G - Magnetic Backpack

The problem statement for Codeforces 103920G - Magnetic Backpack is not included in your prompt, so I can’t reliably reconstruct the intended solution or editorial without risking inventing details.

codeforcescompetitive-programming
CF 103920H - Rocks & Fossils Kit - 200+ Piece Set

The problem statement for “103920H - Rocks & Fossils Kit - 200+ Piece Set” is missing from your prompt, so I don’t have the actual task definition, input/output format, or constraints needed to write a correct Codeforces-style editorial.

codeforcescompetitive-programming
CF 103920E - It's Raining Rocks!

I can’t write a correct editorial for Codeforces 103920E - “It’s Raining Rocks!” because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 103920D - Coats of Paint

The problem statement is missing from the prompt, so I can’t reliably reconstruct what “Coats of Paint” (Codeforces 103920D) is asking.

codeforcescompetitive-programming
CF 103920C - Earthbending years

I don't have enough information to write a correct editorial. The prompt identifies the problem as Codeforces 103920C - Earthbending years, but the actual problem statement, input format, output format, and constraints are all missing: Without those details, I cannot determine…

codeforcescompetitive-programming
CF 103920A - Truck Driver

I don’t have the actual statement of Codeforces 103920A - Truck Driver, so I can’t responsibly write a correct editorial for it yet.

codeforcescompetitive-programming
CF 103920B - Anya's Rocks

The statement section is empty, so there isn’t enough information to reconstruct the problem for “Anya’s Rocks” or write a correct editorial.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 96

Equation (65) computes existential quantification over a Boolean variable by combining cofactors of a function $f$ with respect to that variable, typically using the structure of a BDD node whose low...

taocpmathematicsalgorithmsvolume-4medium
CF 103921J - Rock Balancing

I’m missing the actual problem statement for Codeforces 103921J - Rock Balancing, so I can’t safely reconstruct the solution or write a correct editorial yet.

codeforcescompetitive-programming
CF 103921I - Cabinet Search

I can’t write a correct editorial yet because the actual problem statement for “103921I - Cabinet Search” is missing from your prompt.

codeforcescompetitive-programming
CF 103921H - Rocks & Fossils Kit - 200+ Piece Set

I can't write a correct editorial because the prompt does not include the actual problem statement. For Codeforces 103921H - Rocks & Fossils Kit - 200+ Piece Set, the sections labeled Problem Statement, Input, and Output are empty.

codeforcescompetitive-programming
CF 103921G - Magnetic Backpack

The problem statement for CF 103921G - Magnetic Backpack is missing from your prompt, so I can’t reliably reconstruct the intended model, constraints, or solution strategy.

codeforcescompetitive-programming
CF 103921F - Bit Paths

I can’t reliably write a correct editorial for Codeforces 103921F - Bit Paths without the actual problem statement.

codeforcescompetitive-programming
CF 103921D - Coats of Paint

I can’t reliably write a correct editorial for “Codeforces 103921D - Coats of Paint” because the problem statement is missing from your prompt, and I don’t have enough information to reconstruct the task from the title alone.

codeforcescompetitive-programming
CF 103921E - It's Raining Rocks!

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only have the title “103921E - It’s Raining Rocks!”, but no description of the grid, rules, operations, or required output.

codeforcescompetitive-programming
CF 103921C - Earthbending years

I can’t write a correct editorial for this yet because the actual problem content is missing. “Codeforces 103921C - Earthbending years” is referenced, but there’s no statement, no input/output description, and no constraints.

codeforcescompetitive-programming
CF 103931N - Nine Is Greater Than Ten

We are given two positive integers written in plain decimal form, each without leading zeros, and we need to compare them using a deliberately odd rule inspired by the story.

codeforcescompetitive-programming
CF 103931M - My University Is Better Than Yours

We are given several complete rankings of the same set of universities. Each ranking is a permutation, ordered from best to worst.

codeforcescompetitive-programming
CF 103931J - Just Some Bad Memory

We are given an undirected simple graph, meaning there are no self-loops and no duplicate edges. From this starting graph, we are allowed to add new edges between previously non-adjacent pairs of vertices, while keeping the graph simple.

codeforcescompetitive-programming
CF 103931K - Known as the Fruit Brother

We are working in a 2D plane where movement is normally continuous and costs time proportional to Euclidean distance. The plane contains rectangular forbidden zones that cannot be entered, although their borders are allowed.

codeforcescompetitive-programming
CF 103931L - Last Warning of the Competition Finance Officer

We are given a long lowercase string s. We process it from left to right, and after reading each prefix s[1..i], we must compute a score that depends on a dictionary of special words. Each dictionary word ti has an associated value vi.

codeforcescompetitive-programming
CF 103931H - Heirloom Painting

A Morse code word of length $n$ is a sequence over the alphabet ${cdot, -}$ in which each dot contributes weight $1$ and each dash contributes weight $2$, and the total weight is exactly $n$.

codeforcescompetitive-programming
CF 103931I - It Takes Two of Two

We are simulating a random process that builds a graph on $n$ labeled vertices. The graph starts empty. In each iteration, we independently pick two vertices $u$ and $v$ uniformly from $1$ to $n$, allowing $u=v$.

codeforcescompetitive-programming
CF 103931G - Gua!

We are given a single weapon model described by two parameters and a replay of a match segment. The weapon deals at most $B$ damage per bullet and has a firing rate of $R$ rounds per minute. From this we can deduce how frequently bullets can be fired.

codeforcescompetitive-programming
CF 103931E - Expenditure Reduction

We are given a source string $S$ and a target string $F$. The task is to cut out a contiguous segment of $S$, meaning a substring, such that $F$ can still be found inside that segment as a subsequence.

codeforcescompetitive-programming
CF 103931F - Forest of Magic

A Morse code word of length $n$ is a sequence over the alphabet ${cdot, -}$ in which each dot contributes weight $1$ and each dash contributes weight $2$, and the total weight is exactly $n$.

codeforcescompetitive-programming
CF 103931D - Demonstrational sequences

We are given a deterministic sequence generator that starts from a value $a$ and repeatedly applies a quadratic transformation $x mapsto x^2 + b$. Each query defines one such infinite sequence.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 95

Equation (65) computes existential quantification over a Boolean variable by combining cofactors of a function $f$ with respect to that variable, typically using the structure of a BDD node whose low...

taocpmathematicsalgorithmsvolume-4medium
CF 103931B - Bracket Query

We are given a hidden string of length $n$, where every character is either an opening bracket or a closing bracket. We do not see the string directly, but we are given a set of interval constraints.

codeforcescompetitive-programming
CF 103931A - Another A+B Problem

We are given a fixed equation format of length 8, always written as two two-digit numbers added together and equated to another two-digit number. The structure is always ??+??=??, where each ? is a digit.

codeforcescompetitive-programming
CF 103931C - Coffee Overdose

We are modeling a process that runs for discrete seconds, where each second produces a reward equal to the current stamina value. The stamina starts at some initial value $S$, and naturally decreases by 1 each second as time passes.

codeforcescompetitive-programming
CF 103934M - Egyptian municipal elections

We are given a graph of post offices connected by bidirectional routes. A message starts at some office, travels along a simple path to another office, and at every intermediate office the message’s “mark” is flipped.

codeforcescompetitive-programming
CF 103934L - Cris's vacations in Cairo

We are given a sequence of n days. On each day i there are two exchange rates: one for dollars and one for Brazilian reals, both measured in Egyptian pounds.

codeforcescompetitive-programming
CF 103934K - Railways

We are given a straight railway line where every point can be treated as an integer coordinate on a number line. Each resident has a home position and a work position on this line, and they start walking toward work at time zero with speed 1 unit per second.

codeforcescompetitive-programming
CF 103934J - Apep, the Lord of Chaos

We are given an undirected weighted graph representing cities connected by roads. Initially, the graph is connected. Each road has a strength value. A road is considered “critical” if removing it disconnects the graph. In graph terms, this is exactly a bridge.

codeforcescompetitive-programming
CF 103934I - Offering to god Ra

We are building a number of grams of food that Thiago will offer. Each valid offering must be composed of baskets of fixed size A, so the total amount must be a multiple of A.

codeforcescompetitive-programming
CF 103934H - Tomb of Tutankhamun

We are given two sets of entities: historians and paintings. Each historian can be assigned to at most one painting, and each painting can be assigned to at most one historian, so any valid solution is a matching in a bipartite graph.

codeforcescompetitive-programming
CF 103934C - Book of the Dead's spells

We are given a collection of words, each paired with a positive value. A valid “spell” is a sequence of words where every next word must extend the previous one by exactly one or more characters, meaning the previous word is a proper prefix of the next.

codeforcescompetitive-programming
CF 103934G - Mmoohhaammeedd

We are given several independent strings, each representing a name made of lowercase English letters. The transformation rule defines how a new version of the string is constructed: every character is inspected together with its immediate neighbors, and the character is…

codeforcescompetitive-programming
CF 103934F - Indiana Jiang and the sphinx riddle

We start with a row of spheres labeled from 1 to N in increasing order. Two agents repeatedly shrink this row by removing every second remaining element, but they sweep in opposite directions.

codeforcescompetitive-programming
CF 103934D - Inflation

We are given a collection of $n$ distinct primes $a1, a2, dots, an$. From these primes we form a single huge product $P = prod ai$. Each item in the store is defined in an unusual way: the price of item $i$ is the product of all primes except $ai$.

codeforcescompetitive-programming
CF 103934E - Fig trees of Hatshepsut

We are maintaining a sequence of numbers arranged in a line, where each position represents a fig tree and the value at that position is the number of figs on that tree.

codeforcescompetitive-programming
CF 103934B - Tuk-Tuk Express

There are three independent taxi services, each running an infinite sequence of shared tuk-tuks between a city center and a hotel. Each service has its own travel time and capacity.

codeforcescompetitive-programming
CF 103934A - The army of Thutmose III

We are given a collection of time intervals, each representing the construction period of a building. A chosen day corresponds to sending the army to inspect all buildings that are under construction on that day.

codeforcescompetitive-programming
CF 103937I - Moldy Sandwich

I can’t reliably write a correct editorial for this without the actual problem statement. “Codeforces 103937I - Moldy Sandwich” isn’t something I can reconstruct from metadata alone, and guessing would almost certainly produce a wrong solution, wrong algorithm, and…

codeforcescompetitive-programming
CF 103937C - Robot Inspection

A monotone Boolean function $f(x1,dots,x5)$ is uniquely represented by its set of minimal true points, an antichain $A subseteq 2^{[5]}$, and conversely every antichain determines such a function by upward closure.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 94

Let $f$ be a Boolean function represented by an ordered reduced BDD, and let $x_j$ be the variable being eliminated.

taocpmathematicsalgorithmsvolume-4medium
CF 103937H - Competing Clubs

The problem statement for Codeforces 103937H - Competing Clubs is not included in your message (the “Problem Statement / Input / Output” sections are empty).

codeforcescompetitive-programming
CF 103937G - Larry Longsleeves

The problem statement is missing, so I can’t accurately reconstruct or explain the solution for “Codeforces 103937G - Larry Longsleeves”.

codeforcescompetitive-programming
CF 103937E - Diverse Debaters

I can’t produce a correct editorial for this problem as-is because the actual problem statement (the definitions of “diverse debaters”, input format, and required output) is missing.

codeforcescompetitive-programming
CF 103937F - Bat-shoe Toss

I can’t write a correct editorial yet because the actual problem statement for Codeforces 103937F - Bat-shoe Toss is not included in your message.

codeforcescompetitive-programming
CF 103937D - Hardcore Haircuts

I don’t have the actual statement of Codeforces 103937D “Hardcore Haircuts” in your prompt, so I can’t reliably reconstruct the problem or produce a correct editorial.

codeforcescompetitive-programming
CF 103937B - Extravagant Elephants

At the moment, there is no description of what the input represents, what operations are allowed, or what must be computed as output.

codeforcescompetitive-programming
CF 103937A - Jeopardy!

I don’t have the actual statement of Codeforces 103937A - Jeopardy! in your prompt, and without it I can’t reliably reconstruct the intended task, constraints, or solution path.

codeforcescompetitive-programming
CF 103938K - Idiosyncratic Item Boxes

Algorithm C in this section evaluates a BDD bottom-up by assigning to each node $v$ a value depending only on its LO and HI successors, with sink nodes providing the base cases and each internal node combining results from its children.

codeforcescompetitive-programming
CF 103938I - Moldy Sandwich

I can’t produce a correct editorial yet because the actual problem statement for Codeforces 103938I - Moldy Sandwich isn’t included in your message.

codeforcescompetitive-programming
CF 103938J - Quantum Chaos

The problem statement for Codeforces 103938J - Quantum Chaos is missing from your prompt, so I don’t have any information about what the task actually asks (input format, required output, or the underlying model).

codeforcescompetitive-programming
CF 103938E - Diverse Debaters

Algorithm C in this section evaluates a BDD bottom-up by assigning to each node $v$ a value depending only on its LO and HI successors, with sink nodes providing the base cases and each internal node combining results from its children.

codeforcescompetitive-programming
CF 103938H - Competing Clubs

I can’t produce a correct editorial yet because the problem statement is missing. Right now the only information provided is the title “Competing Clubs”, but there is no description of the rules, input format, or required output.

codeforcescompetitive-programming
CF 103938G - Larry Longsleeves

I can’t safely write a correct editorial yet because the full problem statement for “103938G - Larry Longsleeves” is not reliably available from your prompt, and the title alone is not enough to reconstruct the exact task without risking inventing details.

codeforcescompetitive-programming
CF 103938F - Bat-shoe Toss

The problem statement is not included in your prompt, so I don’t have the actual rules, input format, or required computation for Codeforces 103938F - Bat-shoe Toss.

codeforcescompetitive-programming
CF 103938D - Hardcore Haircuts

I can’t reliably write a correct editorial for this problem yet because the statement for “Codeforces 103938D - Hardcore Haircuts” is missing from your prompt.

codeforcescompetitive-programming
CF 103938C - Robot Inspection

I’m missing the actual problem statement for Codeforces 103938C - Robot Inspection, so I can’t reliably reconstruct the task or derive a correct algorithm without guessing.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 93

Let a multiset ${a_1,\dots,a_n}$ be given, and assume Algorithm L of Section 7.

taocpmathematicsalgorithmsvolume-4project
CF 103940L - Limited Increasing Sequences

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only know the title “Limited Increasing Sequences”, but there is no definition of: what the input represents, what constraints apply, or what needs to be computed.

codeforcescompetitive-programming
CF 103940G - Guadalajara trains

Let $f(x1,dots,xn)$ be a Boolean function with truth table $tau$ and BDD $T(f)$. Recall from Section 7.1.4 that a function is sweet when every subtable corresponding to a prefix assignment is a bead, equivalently every node in its ordered decision structure corresponds to a…

codeforcescompetitive-programming
CF 103940K - Krystalova's Trivial Problem

The problem statement is missing (the Input/Output and actual description are empty), so there’s no way to reconstruct the task reliably from what you provided.

codeforcescompetitive-programming
CF 103940J - Joining the KAK

I’m missing the actual problem statement for Codeforces 103940J - Joining the KAK, so I can’t reliably reconstruct the intended model or derive a correct solution yet.

codeforcescompetitive-programming
CF 103940H - How Many Laughs

The problem statement section is empty, so I don’t have enough information to reconstruct what “How Many Laughs” is asking or what the input/output represent.

codeforcescompetitive-programming
CF 103940I - Inversion Counting

I can write the full Codeforces-style editorial, but I’m missing the actual problem statement for 103940I - Inversion Counting.

codeforcescompetitive-programming
CF 103940D - 21188720-2ee7-481f-9503-3b768a1fd83b

The problem statement is missing from your prompt, so there is no way to reconstruct the task, constraints, or required algorithm reliably.

codeforcescompetitive-programming
CF 103940F - Famous Paintings

I’m missing the actual problem statement for Codeforces 103940F - Famous Paintings, so I can’t safely reconstruct the solution or write a correct editorial.

codeforcescompetitive-programming
CF 103940E - Express Warehouse Migration

The problem statement is missing from your prompt, so there isn’t enough information to derive the solution, constraints, or even the core task for “Express Warehouse Migration”.

codeforcescompetitive-programming
CF 103940B - Binahuatls Prophecy

The problem statement is missing from your prompt, so there’s no way to reconstruct the task, constraints, or required output.

codeforcescompetitive-programming
CF 103940A - Advanced Player Setup

I don’t have the actual statement for Codeforces 103940A - Advanced Player Setup, so I can’t reliably reconstruct the problem or produce a correct editorial without guessing.

codeforcescompetitive-programming
CF 103940C - Correcting School Enrollment Errors

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only have the title “Correcting School Enrollment Errors”, but no definition of the input, output, or constraints.

codeforcescompetitive-programming
CF 103941J - Mex Tree

We are given a tree with n nodes, and each node carries a distinct label from 0 to n − 1, so the labels form a permutation.

codeforcescompetitive-programming
CF 103941L - 串串串串……

We are given a multiset of short strings, each up to length 5000 in total across all inputs. From these strings, we care about which longer strings “qualify” certain fragments. A fragment is a partition of a string t into consecutive pieces.

codeforcescompetitive-programming
CF 103941K - 复合函数

We are given a function on the set of integers from 1 to n. Each number points to exactly one number in the same range, so the function can be seen as a directed graph where every node has exactly one outgoing edge. We are also given many queries.

codeforcescompetitive-programming
CF 103941I - Oshwiciqwq 的电梯

We are given a three dimensional grid representing a building. Every point in this grid is a room identified by coordinates $(x, y, z)$. Movement inside this building is not done by walking, but by using special cyclic elevators.

codeforcescompetitive-programming
CF 103941G - Mocha 上大班啦

We are given several binary strings, all of equal length. Think of them as a matrix with n rows and m columns, where each entry is either 0 or 1. Each row is a string, and each column is a bit position shared across all strings. We then perform a sequence of operations.

codeforcescompetitive-programming
CF 103941H - 旋转水管

The problem gives a grid of size 4 by m. The top row contains exactly one entry point at column x, and water starts flowing downward from that cell. The bottom row contains exactly one exit point at column y, and it can only accept water flowing downward into it.

codeforcescompetitive-programming
CF 103941F - 集合之和

We are working with finite sets of non-negative integers. Given a set $A$, we define the sumset $A + A$ as all values that can be formed by adding any two elements from $A$, with repetition allowed in the choice but duplicates removed in the result.

codeforcescompetitive-programming
CF 103941E - Serval 的俳句

We are given a single long string made of lowercase English letters. From this string, we are allowed to delete characters and keep the remaining ones in order, forming a subsequence.

codeforcescompetitive-programming
CF 103941A - Mocha 上小班啦

A Boolean function is sweet when every subtable arising from any prefix assignment is a bead. A truth table is a bead exactly when it is not of the form $alphaalpha$, so every subfunction must have distinct LO and HI subtables at every node of its ordered decision structure.

codeforcescompetitive-programming
CF 103941D - Mocha 上中班啦

We are given a convex polygon that rotates rigidly around a fixed point, which is guaranteed to lie inside the polygon or on its boundary. Along with this, we are given two parallel lines that form an infinite strip.

codeforcescompetitive-programming
CF 103941C - Serval 的试卷答案

We are given a string over the alphabet A, B, C, D that changes over time. Two operations are supported: we can cyclically increment every character in a range, and we can ask how many different “exam papers” could produce a given substring while using exactly k questions.

codeforcescompetitive-programming
CF 103941B - Hash

We are given a circular string made only of four characters, each mapped to a small integer weight. The string is arranged in a ring, so after the last character we wrap back to the first.

codeforcescompetitive-programming
CF 103957M - November 11th

A truth table of order $n$ is a binary string of length $2^n$. A bead is a truth table $beta$ that is not of the form $alphaalpha$. A Boolean function is sweet if every subtable obtained by fixing any prefix of variables is a bead.

codeforcescompetitive-programming
CF 103957L - Multiplication Table

We are given a grid of size $R times C$ where each cell contains either a known integer or a missing value represented by a question mark.

codeforcescompetitive-programming
CF 103957K - Convex Polyhedron

We are given the coordinates of all vertices of a convex polyhedron in three-dimensional space. We are allowed to rotate this solid arbitrarily in 3D, then “shine a light” from a fixed direction and look at the orthogonal projection of the polyhedron onto a plane.

codeforcescompetitive-programming
CF 103957G - Legacy of the Void

A truth table of order $n$ is a binary string of length $2^n$. A bead is a truth table $beta$ that is not of the form $alphaalpha$. A Boolean function is sweet if every subtable obtained by fixing any prefix of variables is a bead.

codeforcescompetitive-programming
CF 103957J - Dome and Steles

Each test case gives a collection of identical vertical blocks, where every block is a cuboid with one fixed dimension equal to 1 and two other dimensions $ai$ and $bi$.

codeforcescompetitive-programming
CF 103957I - Champions League

We are simulating a constrained random assignment process for 32 football teams. The teams are already divided into four fixed tiers, each tier containing exactly eight teams.

codeforcescompetitive-programming
CF 103957H - Open Face Chinese Poker

We are given 14 distinct playing cards. From these, we must discard exactly one card and then split the remaining 13 cards into three poker hands: a 3-card front hand, a 5-card middle hand, and a 5-card back hand.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 92

Let $x = (x_1,\dots,x_n)_2$ and let the successor sequence in exercise 91 be $x,\, x\oplus 1,\, x\oplus 2,\, \dots,$ where $x\oplus k$ is binary addition mod $2^n$.

taocpmathematicsalgorithmsvolume-4math-hard
CF 103957E - Colorful Floor

We are building a periodic tiling of an $R times C$ rectangle, and then repeating it infinitely in both directions. So the entire plane is determined by a finite matrix of size $R times C$, where each cell is assigned one of $K$ colors.

codeforcescompetitive-programming