Codeforces Global Round 25

Solutions for Codeforces Global Round 25 (contest 1951). 1/9 problems verified against sample I/O. Difficulty range: 900-3200.

9 items

Codeforces Global Round 25

Type: Global | Problems: 9 | Verified: 1/9 | Rating range: 900-3200 | Time: 11m 49s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Dual Trigger	900	constructive-algorithms, greedy, math	51s	✓
B	Battle Cows	1200	binary-search, data-structures, greedy	1m 24s	✗
C	Ticket Hoarding	1400	greedy, math, sortings	59s	✗
D	Buying Jewels	2000	constructive-algorithms, greedy, math	1m 19s	✗
E	No Palindromes	2000	brute-force, constructive-algorithms, divide-and-conquer	1m 1s	✗
F	Inversion Composition	2500	constructive-algorithms, data-structures, greedy	1m 56s	✗
G	Clacking Balls	3100	combinatorics, math, probabilities	1m 25s	✗
H	Thanos Snap	3200	binary-search, dp, games	1m 17s	✗
I	Growing Trees	3200	binary-search, constructive-algorithms, flows	1m 37s	✗

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CF 1951A - Dual Trigger

We are given a row of lamps, all initially off. We can perform one type of operation any number of times: choose two lamps that are currently off and are not next to each other, and turn them both on simultaneously.

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CF 1951B - Battle Cows

We have a line of cows, each with a unique Cowdeforces rating, and they compete in a sequential tournament. The tournament begins with the first two cows, and each subsequent match is between the winner of the previous match and the next cow in line.

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CF 1951C - Ticket Hoarding

The task is to buy exactly k concert tickets over n days, with each day offering a ticket price ai. You are limited to buying at most m tickets per day. Additionally, every ticket you buy increases the price of all future tickets by the number of tickets bought on that day.

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CF 1951D - Buying Jewels

We are given a buyer who starts with a fixed number of coins. A shop is not fixed in advance; instead, we are allowed to design up to 60 sequential stalls. Each stall has an unlimited supply of jewels, and a fixed integer price per jewel.

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CF 1951E - No Palindromes

We are given a string and we are allowed to cut it into contiguous pieces. The goal is to decide whether we can cut it so that every resulting piece is not a palindrome. If it is possible, we must also construct one such cut.

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CF 1951F - Inversion Composition

We are asked to construct a permutation q of size n such that the sum of inversions of q and the composition q ∘ p equals a given target k. The input permutation p is fixed, and inversions count how many pairs of indices are out of order.

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CF 1951G - Clacking Balls

We are given a circle of baskets numbered from 1 to $m$, and $n$ balls initially placed in distinct baskets. Alice repeatedly chooses one of the balls uniformly at random and moves it clockwise to the next basket.

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CF 1951H - Thanos Snap

We are given an array whose length is a power of two, and it initially contains all integers from 1 to $2^k$ exactly once. So the array is just a permutation, but its initial order matters. A game is played on this array. A parameter $t$ is fixed first.

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CF 1951I - Growing Trees

We are given a connected simple undirected graph with up to 50 vertices and at most 50 edges. Each edge can be used multiple times in a constructed multigraph, and we control how many copies of each edge we create through a non-negative integer array $x$.