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tamnd's digital brain — notes, problems, research

41541 notes

CF 102899C - KK 算日期

Let $n ge m ge 1$ and let $a1 ge a2 ge cdots ge am ge 1$ be a partition of $n$ such that $ Indeed, if $a1$ is the maximum part and $am$ is the minimum part, the condition gives $a1 - am le 1$, hence $am in {a1, a1 - 1}$. Therefore every part equals either $a1$ or $a1 - 1$.

codeforcescompetitive-programming
CF 102899H - KK 与十佳

We are given a list of integers representing scores assigned by judges. All values are nonzero and all are distinct. We are allowed to remove exactly one of these numbers. After removing it, we multiply all remaining numbers together, and that product becomes the final score.

codeforcescompetitive-programming
CF 102899I - KK 买股票

We are given a sequence of stock prices over n days. On each day i, the stock has a known price p[i]. KK is allowed to perform at most one complete transaction: he may buy once on some day and later sell once on a strictly later day.

codeforcescompetitive-programming
CF 102899G - KK 看跳舞

We are given multiple test cases. Each test case describes a sequence of $n$ distinct integers, which is a permutation of $1 ldots n$. The sequence represents the order in which dancers pass in front of an observer.

codeforcescompetitive-programming
CF 102899F - KK 与刷题

We are given a sequence of days, and on each day kk records how many wrong answers (WA) he made. These values form an array a[1..n]. Starting from a score of zero, the score evolves day by day. When processing day i, we compare the WA count a[i] with every previous day j < i.

codeforcescompetitive-programming
CF 102899D - KK 与卡牌

We are given two collections of heroes represented as cards. Each card has a short name, a string of lowercase letters, and a strength value written as a decimal number.

codeforcescompetitive-programming
CF 102899E - KK 与答辩

We are given several independent test cases. In each test case, there are multiple “defense sessions”. In every session, a list of students appears, and each student has a combined score computed as the sum of two components.

codeforcescompetitive-programming
CF 102899B - KK 学几何

We are given a stream of geometric figures, each described by a type identifier followed by its dimensions. Every figure contributes an area, and the task is to accumulate the total area across all figures and output the final sum rounded to one decimal place.

codeforcescompetitive-programming
CF 102899A - KK 画猪

The task is intentionally minimal: the program receives a single token on standard input and must respond with a fixed ASCII drawing of a pig.

codeforcescompetitive-programming
CF 102900K - Traveling Merchant

Let $n ge m ge 1$ and let $a1 ge a2 ge cdots ge am ge 1$ be a partition of $n$ such that $ Indeed, if $a1$ is the maximum part and $am$ is the minimum part, the condition gives $a1 - am le 1$, hence $am in {a1, a1 - 1}$. Therefore every part equals either $a1$ or $a1 - 1$.

codeforcescompetitive-programming
CF 102900J - Octasection

We are given a collection of axis-aligned 3D boxes in space. Each box represents a solid region defined by independent intervals on the x, y, and z axes. Boxes may overlap in any way.

codeforcescompetitive-programming
CF 102900M - Gitignore

I can’t write a correct editorial for “Codeforces 102900M - Gitignore” because the actual problem statement is missing from your prompt. Right now I don’t know what the input represents, what operations are allowed, or what the output should compute.

codeforcescompetitive-programming
CF 102900L - Traveling in the Grid World

The problem statement is missing from your prompt, so I don’t have the actual rules for the grid world (movement rules, goals, constraints, etc.). Without that, any editorial would be fabricated and likely useless.

codeforcescompetitive-programming
CF 102900H - Rice Arrangement

I can’t write a correct editorial for this yet because the actual problem statement for Codeforces 102900H - Rice Arrangement is missing from your prompt.

codeforcescompetitive-programming
CF 102900B - Mine Sweeper II

Let $n ge m ge 1$ and let $a1 ge a2 ge cdots ge am ge 1$ be a partition of $n$ such that $ Indeed, if $a1$ is the maximum part and $am$ is the minimum part, the condition gives $a1 - am le 1$, hence $am in {a1, a1 - 1}$. Therefore every part equals either $a1$ or $a1 - 1$.

codeforcescompetitive-programming
CF 102900I - Sky Garden

I can’t write a correct editorial without the actual problem statement. Right now the “Problem Statement / Input / Output” sections are empty, and Codeforces solutions are entirely driven by the precise structure of the task.

codeforcescompetitive-programming
CF 102900F - Fountains

The problem works with a sequence of values arranged on a line, where each value represents the “weight” of a unit segment. From these values we can compute the sum of any contiguous segment, which we will call its segment weight.

codeforcescompetitive-programming
CF 102900G - Fibonacci

The problem statement is missing from your prompt, so I don’t actually know what Codeforces 102900G - Fibonacci is asking. Right now I only see the title, but no definition of the input, output, or task.

codeforcescompetitive-programming
CF 102900E - The Journey of Geor Autumn

The problem statement is missing from your prompt (the “Problem Statement / Input / Output” sections are empty), so there’s no way to reconstruct Codeforces 102900E reliably.

codeforcescompetitive-programming
CF 102900D - Walker

We are given a one-dimensional segment from 0 to n. Two walkers start somewhere on this segment. Each walker has its own starting position and its own constant speed, and both are allowed to walk back and forth along the segment, but they can never step outside the interval.

codeforcescompetitive-programming
CF 102900A - Wowoear

The task describes a geometric race path made of straight segments connected end to end in the plane. A runner starts at the first point of a polyline and must follow the segments in order until the last point.

codeforcescompetitive-programming
CF 102900C - Sum of Log

We are given two integers $X$ and $Y$, and we consider all pairs $(i, j)$ where $0 le i le X$ and $0 le j le Y$. For each pair, we only care about those where the bitwise AND of the two numbers is zero, meaning the two numbers never share a common set bit.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 22

Let $E(q)=\prod_{m\ge 1}(1-q^m).$ Euler’s pentagonal number theorem gives $E(q)=\sum_{k\in \mathbb{Z}} (-1)^k q^{k(3k-1)/2}.$ Let $S(q)=\sum_{n\ge 1} \sigma(n) q^n.$

taocpmathematicsalgorithmsvolume-4hm-medium
CF 102904D - Funny Cost

I can’t write a correct editorial for “Codeforces 102904D - Funny Cost” because the actual problem statement (definition of the input, cost function, and required output) is missing.

codeforcescompetitive-programming
CF 102904B - Dispatch Money

We are given a sequence of monetary requests that must be satisfied in order, and a fixed amount of available money that starts at zero. Each request either increases or decreases the available balance, and the process evolves step by step as we move through the sequence.

codeforcescompetitive-programming
CF 102906C - Дивизионы

Let $T(m1,dots,mn)$ be the $n$-dimensional torus with cross order as in Section 7.2.1.3, and let Theorem W be the structural statement whose proof in Exercises 91-92 relies on the spread function $alpha$ behaving uniformly across coordinates.

codeforcescompetitive-programming
CF 102906F - Не подпоследовательность

We are given a string consisting of lowercase letters. The task is to construct the shortest possible string that cannot be obtained as a subsequence of the given string.

codeforcescompetitive-programming
CF 102906E - Сумма

We are given a sequence of numbers, but instead of treating them as individual values, we should think of them as a multiset where we are allowed to repeatedly perform a very specific transformation.

codeforcescompetitive-programming
CF 102906D - Пары, свободные от квадратов

We are given a sequence of integers and we want to count how many pairs of positions can be chosen so that the product of the two corresponding values does not contain any squared prime factor. Another way to phrase the condition is to look at prime factorizations.

codeforcescompetitive-programming
CF 102906A - Класс

We can reinterpret the input as a graph. Each vertex represents an item in the class, and each edge represents that two items are compatible.

codeforcescompetitive-programming
CF 102906B - Лестница из чисел

I can’t write a correct editorial for this yet because the problem statement is missing. “Codeforces 102906B - Лестница из чисел” alone isn’t enough to reconstruct the task reliably, and guessing would very likely produce the wrong solution and reasoning.

codeforcescompetitive-programming
CF 102911K - Kallipolis

We are given a list of philosophers, each associated with a positive integer value that represents their “strength of dominance.

codeforcescompetitive-programming
CF 102911J - Junior Prom

We are given a set of students, and several student organizations. Each organization consists of a group of officers, and every officer must be physically present for their organization’s prom in order for the event to run.

codeforcescompetitive-programming
CF 102911I - Implementation Problem

I can’t write a correct Codeforces-style editorial for “102911I - Implementation Problem” without the actual problem statement.

codeforcescompetitive-programming
CF 102911F - Folklore

We are given a sequence of distinct items, each item originally sitting in a fixed position from 1 to N. We must rearrange them into a new ordering.

codeforcescompetitive-programming
CF 102916J - Lost Island

Let $a1 ge a2 ge cdots ge am ge 1$ be a partition of $n$ into $m$ parts that is optimally balanced, meaning $ Let $t$ be the number of parts equal to $x$ and $m-t$ the number of parts equal to $x-1$. The partition has total sum $$n = tx + (m-t)(x-1) = mx - (m-t).

codeforcescompetitive-programming
CF 102916N - Premove Checkmate

We are given a very specific chess endgame situation: white has only a king and a queen, while black has only a king. The white king starts on a fixed square c3 and the white queen starts on d4.

codeforcescompetitive-programming
CF 102916M - Binary Search Tree

We are given an undirected tree with vertices labeled from 1 to n. We are allowed to choose any vertex as the root and then orient every edge away from it, turning the tree into a rooted structure.

codeforcescompetitive-programming
CF 102916L - Not the Longest Increasing Subsequence

We are given a sequence of length $n$, where every value lies between $1$ and $k$. We are allowed to remove some elements, and after removal we look at the longest strictly increasing subsequence of the remaining array.

codeforcescompetitive-programming
CF 102916K - Bloodseeker

We are given a character who survives over a timeline measured in seconds. At the start he has some maximum health cap and an initial amount of health. Every second that passes reduces his health by one unit, and if his health ever becomes zero he is considered dead.

codeforcescompetitive-programming
CF 102916I - Chess Tournament

We are organizing a complete round-robin chess tournament among n players, meaning every pair of players must meet exactly once. That creates a fixed set of n(n−1)/2 games, and the only flexibility we have is how to schedule them over time.

codeforcescompetitive-programming
CF 102916H - Video Reviews - 2

We are given a sequence of videobloggers in a fixed order. Each blogger has a threshold value a[i]. When we approach bloggers from left to right, a blogger will record a review automatically only if either they are explicitly convinced by the marketer, or the number of reviews…

codeforcescompetitive-programming
CF 102916C - Cyclically Shifted Maze

Let $a1 ge a2 ge cdots ge am ge 1$ be a partition of $n$ into $m$ parts that is optimally balanced, meaning $ Let $t$ be the number of parts equal to $x$ and $m-t$ the number of parts equal to $x-1$. The partition has total sum $$n = tx + (m-t)(x-1) = mx - (m-t).

codeforcescompetitive-programming
CF 102916G - Lexicographically Minimal Subsequence

We are given a single string and a number k. From this string we are allowed to delete characters while preserving the relative order of the remaining characters.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 21

Let F(a,b;u,v)=\sum_{k,l\ge 0} u^k v^l z^{kl} \frac{(z-az)(z-az^2)\cdots(z-az^k)}{(1-z)(1-z^2)\cdots(1-z^k)} \frac{(z-bz)(z-bz^2)\cdots(z-bz^l)}{(1-z)(1-z^2)\cdots(1-z^l)}.

taocpmathematicsalgorithmsvolume-4math-medium
CF 102916F - Exactly One Point

We are given a collection of segments on a number line, and each segment spans between two even integers. The task is to place a set of points on the same line so that every segment contains exactly one chosen point, while also ensuring that every chosen point lies inside at…

codeforcescompetitive-programming
CF 102916E - Powerless Mage

We are given a collection of spells, each spell consumes some combination of three types of mana: blue, purple, and orange. A mage has a total pool of these three colors, and what matters is only the total amount of mana across all colors, not the individual distribution.

codeforcescompetitive-programming
CF 102916D - Two Pirates - 2

We are given a collection of treasures, each with a positive value. Two players take turns picking remaining items until none are left. One player is fully strategic and wants to maximize the total value he obtains.

codeforcescompetitive-programming
CF 102916A - Absenteeism

We are given a day that spans a time segment from 0 to m. There are n coworkers, and each coworker i is present only during their own interval from ai to bi. Alex must choose a continuous working interval [x, y] inside the day.

codeforcescompetitive-programming
CF 102916B - Fakes and Shidget

Each step of the process is identical in structure. Pavel is repeatedly matched with a random character, chosen uniformly from a fixed set of $n$. When he meets character $i$, he must immediately pick exactly one of two quests.

codeforcescompetitive-programming
CF 102920K - Tiling Polyomino

We are given a shape on an $n times n$ grid, described by cells marked as belonging to a polyomino. The shape is connected, has no holes, and every cell has at least two neighboring cells inside the shape. So locally, nothing behaves like a leaf or dead-end.

codeforcescompetitive-programming
CF 102920L - Two Buildings

We are given a sequence of building heights arranged in a straight line, each position having a building of width 1.

codeforcescompetitive-programming
CF 102920F - Ink Mix

Let $a1 ge a2 ge cdots ge am ge 1$ be a partition of $n$ into $m$ parts that is optimally balanced, meaning $ Let $t$ be the number of parts equal to $x$ and $m-t$ the number of parts equal to $x-1$. The partition has total sum $$n = tx + (m-t)(x-1) = mx - (m-t).

codeforcescompetitive-programming
CF 102920J - Switches

We are given a system with the same number of switches and lights, and a binary connection matrix describing how switches influence lights.

codeforcescompetitive-programming
CF 102920I - Stock Analysis

We are given a sequence of daily stock fluctuation values. Each value represents the change from one day to the next, so any contiguous segment represents the total change over a continuous time window. For each query, we restrict ourselves to a subarray interval $[S, E]$.

codeforcescompetitive-programming
CF 102920H - Needle

The border between the two kingdoms is made of three horizontal lines, stacked one above another with equal vertical spacing. Each line has several “holes”, each located at an integer position along the horizontal axis.

codeforcescompetitive-programming
CF 102920G - Mobile Robot

We are given a line with $n$ robots, each starting at some real coordinate. We must relocate them so that after movement they form a perfectly regular chain: robot $i+1$ must be exactly distance $d$ to the right of robot $i$.

codeforcescompetitive-programming
CF 102920E - Imprecise Computer

We are given a sequence of integers of length $n$, and we are told to imagine it as a derived statistic from a peculiar tournament on the set ${1,2,dots,n}$. In this tournament, every pair of distinct numbers is compared twice.

codeforcescompetitive-programming
CF 102920D - Electric Vehicle

We are given a complete graph whose vertices are villages placed on a 2D grid. The cost of traveling between two villages is not fixed in advance as an edge weight in the usual sense, but instead comes from energy consumption: moving between two points consumes energy equal to…

codeforcescompetitive-programming
CF 102920A - Autonomous Vehicle

Algorithm H generates all integer partitions $a1 ge cdots ge am ge 1$ of $n$ by maintaining a weakly decreasing sequence whose entries are positive and whose sum is always $n$.

codeforcescompetitive-programming
CF 102920C - Dessert Café

We are given a weighted tree where each node is a candidate location for a café, and a subset of nodes are marked as apartment complexes. The distance between any two nodes is the sum of edge weights along their unique path in the tree.

codeforcescompetitive-programming
CF 102920B - Commemorative Dice

We are given two cubes, each with six faces. Every face contains a positive integer, and for each cube the six values sum to 21. When the cube is rolled, each face is equally likely to appear, so each cube defines a uniform probability distribution over its six face values.

codeforcescompetitive-programming
CF 1029352 - Разбиение таблицы

Algorithm H generates all integer partitions $a1 ge cdots ge am ge 1$ of $n$ by maintaining a weakly decreasing sequence whose entries are positive and whose sum is always $n$.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 20

Let F(a,b;u,v)=\sum_{k,l\ge 0} u^k v^l z^{kl} \frac{(z-az)(z-az^2)\cdots(z-az^k)}{(1-z)(1-z^2)\cdots(1-z^k)} \frac{(z-bz)(z-bz^2)\cdots(z-bz^l)}{(1-z)(1-z^2)\cdots(1-z^l)}.

taocpmathematicsalgorithmsvolume-4math-medium
CF 1029354 - Антенна

The problem statement section is empty, so I don’t actually have the rules of what “Антенна” is asking for. Writing a correct Codeforces editorial without the task definition would force me to guess the problem, which would make the solution unreliable.

codeforcescompetitive-programming
CF 1029353 - Изменённая ДНК

I can’t write a correct Codeforces editorial for this yet because the actual problem statement is missing. Right now I only see the title “Изменённая ДНК” (“Modified DNA”), but no definition of the input, operations, or what needs to be computed.

codeforcescompetitive-programming
CF 1029351 - Два станка

I can absolutely write this editorial in the required Codeforces style, but I’m missing the actual problem statement for “1029351 - Два станка”.

codeforcescompetitive-programming
CF 1029365 - Календарь на Альфе Центавра

Algorithm H generates all integer partitions $a1 ge cdots ge am ge 1$ of $n$ by maintaining a weakly decreasing sequence whose entries are positive and whose sum is always $n$.

codeforcescompetitive-programming
CF 1029368 - A+B

The task is to read two integer values and compute their sum. The input consists of two numbers presented in a simple textual format, and the output is a single integer representing their arithmetic addition. There is no hidden structure such as graphs, sequences, or queries.

codeforcescompetitive-programming
CF 1029366 - Числа

The problem statement is missing from the prompt, so there’s no way to reconstruct a correct editorial yet. “Codeforces 1029366 - Числа” is not enough to determine what is being asked (there are many standard “numbers” problems: digit DP, divisibility, counting…

codeforcescompetitive-programming
CF 1029367 - Хорошие раскраски

The problem statement section is empty, so there isn’t enough information to write a correct editorial. For Codeforces editorials, I need at least the full statement (or a link / text describing inputs, outputs, and constraints).

codeforcescompetitive-programming
CF 102939A - Imitation Game

Algorithm H generates all integer partitions $a1 ge cdots ge am ge 1$ of $n$ by maintaining a weakly decreasing sequence whose entries are positive and whose sum is always $n$.

codeforcescompetitive-programming
CF 102939G - Ski-Bot 3000

The task is to navigate a robot across a rectangular grid representing a ski slope, moving from the left side of the grid to the right side. Each cell is either blocked, normal snow, or a ramp.

codeforcescompetitive-programming
CF 102939F - Factory Batching

I can’t write a correct editorial for this yet because the actual problem content is missing. “Codeforces 102939F - Factory Batching” is referenced, but there’s no statement, no constraints, and no description of the input/output or rules.

codeforcescompetitive-programming
CF 102939D - Robot Toss

Two robots stand at two fixed lattice points on a grid. They throw a ball back and forth, and the ball travels along the straight line segment connecting their positions. A third point, Eve, is trying to intercept the ball.

codeforcescompetitive-programming
CF 102939E - Decryption Scheme

I can’t reliably write a correct editorial for Codeforces 102939E - Decryption Scheme without the actual problem statement.

codeforcescompetitive-programming
CF 102939B - Pathfinder

I’m missing the actual problem statement for Codeforces 102939B - Pathfinder, so I can’t safely reconstruct the logic or write a correct editorial without risking inventing details.

codeforcescompetitive-programming
CF 102939C - Robot Snowman

I can’t reliably write a correct Codeforces editorial for “102939C - Robot Snowman” because the actual problem statement (inputs, outputs, and rules) is missing from your prompt.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 19

Let F(a,b;u,v)=\sum_{k,l\ge 0} u^k v^l z^{kl} \frac{(z-az)(z-az^2)\cdots(z-az^k)}{(1-z)(1-z^2)\cdots(1-z^k)} \frac{(z-bz)(z-bz^2)\cdots(z-bz^l)}{(1-z)(1-z^2)\cdots(1-z^l)}.

taocpmathematicsalgorithmsvolume-4math-medium
CF 102940C - Robot Snowman

Algorithm H generates all integer partitions $a1 ge cdots ge am ge 1$ of $n$ by maintaining a weakly decreasing sequence whose entries are positive and whose sum is always $n$.

codeforcescompetitive-programming
CF 102940I - Artbot

We are given a tree rooted at node 1, and a robot that performs a constrained walk starting from this root. The robot always starts by visiting node 1 and marking it as painted.

codeforcescompetitive-programming
CF 102940J - EvilCorp

I can absolutely write that editorial in the style you want, but I’m missing the only thing that makes it possible: the actual problem content.

codeforcescompetitive-programming
CF 102940F - Factory Batching

I can’t write a correct Codeforces-style editorial without the actual problem statement. Right now the “Problem Statement / Input / Output” sections are empty, so any solution would be guesswork and would almost certainly be wrong.

codeforcescompetitive-programming
CF 102940H - Factory Tasks

I can absolutely write this editorial, but I’m missing the one thing that makes it possible to be correct: the actual statement of Codeforces 102940H - Factory Tasks.

codeforcescompetitive-programming
CF 102940G - Ski-Bot 3000

The problem statement is empty in what you provided, so there is no way to reconstruct the actual task, constraints, or required algorithm for “Ski-Bot 3000”.

codeforcescompetitive-programming
CF 102940E - Decryption Scheme

I don’t have the actual statement of Codeforces 102940E - Decryption Scheme, and I can’t reliably reconstruct it from the title alone without risking inventing details.

codeforcescompetitive-programming
CF 102940D - Robot Toss

I can write the full Codeforces-style editorial, but I am missing the actual problem statement for Codeforces 102940D - Robot Toss.

codeforcescompetitive-programming
CF 102942A - Directional Move

Algorithm H generates all integer partitions $a1 ge cdots ge am ge 1$ of $n$ by maintaining a weakly decreasing sequence whose entries are positive and whose sum is always $n$.

codeforcescompetitive-programming
CF 102942F - Offer

The brute-force viewpoint starts naturally by fixing a segment [l, r]. Inside it, we group positions by value. If we decide to include a value v, we must pay at least one occurrence of v inside the segment, so the cost contribution of v is the minimum ai over all i in the…

codeforcescompetitive-programming
CF 102942E - Password

I can’t reliably write a correct editorial for Codeforces 102942E - Password because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 102942D - XOR Game

I don’t have the actual statement of Codeforces 102942D - XOR Game in your prompt, and that problem ID doesn’t correspond to a standard indexed CF problem I can reliably reconstruct.

codeforcescompetitive-programming
CF 102942B - Make All Odd

We are given a sequence of integers and we are allowed to perform a simple operation that modifies elements so that, after applying it any number of times, we want every element in the sequence to become odd.

codeforcescompetitive-programming
CF 102942C - Team

I can’t write a correct editorial for Codeforces 102942C - Team without the actual problem statement. That contest ID isn’t something I can reliably reconstruct from memory alone, and guessing would very likely produce a wrong solution and misleading reasoning.

codeforcescompetitive-programming
CF 102944J - Jackson

Algorithm H generates all integer partitions $a1 ge cdots ge am ge 1$ of $n$ by maintaining a weakly decreasing sequence whose entries are positive and whose sum is always $n$.

codeforcescompetitive-programming
CF 102944I - Isle Royale

We are given a weighted undirected graph where vertices represent locations on an island and edges represent paths between them. The hero starts at node 1 and wants to reach node N. Traveling along an edge takes one minute and consumes energy equal to the edge weight.

codeforcescompetitive-programming
CF 102944H - Holland

We are given a stream of customers who arrive over time at a single counter. Each customer has an arrival time and a tip value. If a customer is accepted, they join a FIFO line and are served one by one, with each service taking exactly the same fixed amount of time.

codeforcescompetitive-programming
CF 102944B - Bois Blanc

Let the $2times 2times 3$ torus be the Cartesian product $$T = mathbb{Z}2 times mathbb{Z}2 times mathbb{Z}3,$$ so each element is a triple $(x,y,z)$ with $x,y in {0,1}$ and $z in {0,1,2}$, with arithmetic taken modulo $2,2,3$ respectively. This gives $12$ vertices.

codeforcescompetitive-programming
CF 102944G - Grand Rabbits

We are given a single array of positive weights along a line, representing how much delivery load each rabbit family contributes. Each day, we are given a contiguous segment of this array, and we must split that segment into exactly $k$ contiguous groups.

codeforcescompetitive-programming
CF 102944F - Flint

We are given a small collection of positive integers. From this collection, we consider every possible non-empty subset and compute the greatest common divisor of the numbers inside that subset. A subset is considered “valid” if this gcd equals exactly 1.

codeforcescompetitive-programming
CF 102944D - Detroit

We are given a directed graph representing a city road system, where each road can only be used in one direction and every road has unit cost in the sense that we will eventually count how many roads we decide to keep.

codeforcescompetitive-programming