Codeforces Round 919 (Div. 2)

Solutions for Codeforces Round 919 (Div. 2) (contest 1920). 3/7 problems verified against sample I/O. Difficulty range: 800-3000.

7 items

Codeforces Round 919 (Div. 2)

Type: Div. 2 | Problems: 7 | Verified: 3/7 | Rating range: 800-3000 | Time: 12m 20s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Satisfying Constraints	800	brute-force, greedy, math	2m 3s	✓
B	Summation Game	1100	games, greedy, math	1m 49s	✓
C	Partitioning the Array	1600	brute-force, math, number-theory	48s	✗
D	Array Repetition	1900	binary-search, brute-force, dsu	1m 18s	✓
E	Counting Binary Strings	2100	combinatorics, dp, math	3m 10s	✗
F1	Smooth Sailing (Easy Version)	2500	binary-search, brute-force, data-structures	50s	✗
F2	Smooth Sailing (Hard Version)	3000	binary-search, data-structures, dsu	2m 22s	✗

Practice › Codeforces Solutions › Codeforces Round 919 (Div. 2) ›

CF 1920E - Counting Binary Strings

We are asked to count the number of binary strings such that the total number of substrings containing exactly one 1 equals a given number n, and no such substring has length exceeding a given maximum k. A substring is simply a consecutive portion of the string.

Practice › Codeforces Solutions › Codeforces Round 919 (Div. 2) ›

CF 1920F2 - Smooth Sailing (Hard Version)

We are given a rectangular grid where some cells are islands, some are open ocean, and some are underwater volcanoes. Thomas wants to sail in loops that fully encircle the island without stepping onto it.

Practice › Codeforces Solutions › Codeforces Round 919 (Div. 2) ›

CF 1920F1 - Smooth Sailing (Easy Version)

We are given a 2D grid representing an island in the ocean. Each cell can be part of the island (), open ocean (.), or an underwater volcano (v). The island cells form a single contiguous shape not touching the grid edges.

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CF 1920D - Array Repetition

We start with an empty sequence and gradually build a very large array using two kinds of operations. The first operation appends a single value to the end, effectively extending the sequence by one element.

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CF 1920A - Satisfying Constraints

We are asked to determine how many integers satisfy a set of constraints. Each test case consists of multiple constraints on a single integer $k$. The constraints fall into three categories: $k$ must be at least $x$, $k$ must be at most $x$, and $k$ must not equal $x$.

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CF 1920B - Summation Game

We are asked to simulate a two-step game played on an array of positive integers. The first player, Alice, can remove up to $k$ elements. She wants the final sum of the array to be as large as possible.

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CF 1920C - Partitioning the Array

This is a Type B problem, a proof of existence. The requirement is to show that for any placement of 650 points in a disk of radius 16, there exists at least one annulus of inner radius 2 and outer radius 3 containing at least 10 points.