Codeforces Round 920 (Div. 3)

Solutions for Codeforces Round 920 (Div. 3) (contest 1921). 4/7 problems verified against sample I/O. Difficulty range: 800-2200.

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Codeforces Round 920 (Div. 3)

Type: Div. 3 | Problems: 7 | Verified: 4/7 | Rating range: 800-2200 | Time: 14m 56s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Square	800	greedy, math	1m 57s	✓
B	Arranging Cats	800	greedy, implementation	2m 3s	✓
C	Sending Messages	900	greedy, math	1m 48s	✓
D	Very Different Array	1100	data-structures, greedy, sortings	2m 24s	✓
E	Eat the Chip	1600	brute-force, games, greedy	2m 27s	✗
F	Sum of Progression	1900	brute-force, data-structures, dp	2m 2s	✗
G	Mischievous Shooter	2200	brute-force, data-structures, divide-and-conquer	2m 15s	✗

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CF 1921G - Mischievous Shooter

We are given a grid of size $n times m$, each cell either containing a target represented by or empty represented by .. Shel has a shotgun that fires in one of four diagonal directions: right-down, left-down, left-up, or right-up.

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CF 1921E - Eat the Chip

We have a two-player game on a rectangular grid with height h and width w. Alice’s chip starts at (xa, ya) and can move down, down-left, or down-right. Bob’s chip starts at (xb, yb) and moves up, up-left, or up-right.

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CF 1921D - Very Different Array

We have an array a of length n. Another array b contains m values, where m is at least n. We are allowed to choose exactly n elements from b, then arrange those chosen elements in any order to form a new array c.

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CF 1921F - Sum of Progression

We are given an array of integers and a set of queries. Each query specifies a starting index s, a step size d, and a count k. For a query, we must sum k elements of the array taken at indices s, s+d, s+2d, ...

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CF 1921B - Arranging Cats

The task is to transform an initial arrangement of cats in boxes into a target arrangement using the fewest operations. Each box either contains a cat or is empty, and the initial state is given by a binary string s, while the target state is given by a binary string f.

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CF 1921A - Square

We are given the four vertices of a square on a 2D coordinate plane. The points are presented in arbitrary order, so we do not know which point is the bottom-left corner, top-right corner, and so on. The square has two special properties.

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CF 1921C - Sending Messages

Stepan needs to send a series of messages at strictly increasing moments in time. His phone starts with a finite charge, loses a constant amount per unit of time while it is on, and consumes a fixed cost if he turns it off and then back on.