Codeforces Global Round 9

9 problems from Codeforces Global Round 9 (contest 1375), difficulty 1100-3500. 1/9 solutions verified against sample I/O.

9 items

Codeforces Global Round 9

Global | 9 problems | 1/9 verified | Difficulty 1100-3500 | 36m 35s

# Problem Rating Tags Accepted Time ✓
A Sign Flipping 1100 constructive-algorithms, math 18,842 2m 18s
B Neighbor Grid 1200 constructive-algorithms, greedy 17,850 2m 18s
C Element Extermination 1400 constructive-algorithms, data-structures, greedy 22,944 2m 34s
D Replace by MEX 1900 brute-force, constructive-algorithms, sortings 10,140 1m 24s
E Inversion SwapSort 2500 constructive-algorithms, greedy, sortings 3,370 5m 30s ✓
F Integer Game 2600 constructive-algorithms, games, interactive 2,510 6m 23s
G Tree Modification 2800 brute-force, constructive-algorithms, dfs-and-similar 2,187 2m 29s
H Set Merging 3300 constructive-algorithms, divide-and-conquer 496 5m 47s
I I 3500 geometry, math, matrices 277 7m 52s
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geometry math matrices number theory Jun 14, 2026
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CF 1375D - Replace by MEX

We are given several arrays, each containing integers in the range from zero up to the array length. We are allowed to repeatedly pick a position in the array and overwrite its value with the current MEX of the entire array.
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CF 1375H - Set Merging

We are given a permutation of numbers from 1 to n, but the real object we care about is not the values themselves, it is their positions. Initially each position i forms a singleton set containing the value a[i].
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CF 1375F - Integer Game

Three numbers represent the sizes of three piles of stones. The interaction alternates between us and the opponent.
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CF 1375E - Inversion SwapSort

We are given a sequence of numbers, and we are allowed to swap any two positions, but only if those two positions currently form an inversion in the original array. An inversion is simply a pair of indices where the left value is strictly larger than the right value.
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CF 1375A - Sign Flipping

Stopped thinking
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CF 1375B - Neighbor Grid

We are given a grid of integers, but the final goal is not to preserve these values exactly. Instead, we are allowed to only increase values, and we want to transform the grid into a configuration where every positive cell behaves like a “node” whose value equals how many of…
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CF 1375G - Tree Modification

Let $Nge 1$ be fixed. An $m$-survivor is a positive integer all of whose prime factors exceed $m$. Let $$f(x,m)={nle x:text{$n$ is an $m$-survivor}},$$ and let $$fk(x,m)={nle x:text{$n$ is an $m$-survivor having exactly $k$ prime factors}},$$ where prime factors are counted…
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CF 1375C - Element Extermination

Let $Nge 1$ be fixed. An $m$-survivor is a positive integer all of whose prime factors exceed $m$. Let $$f(x,m)={nle x:text{$n$ is an $m$-survivor}},$$ and let $$fk(x,m)={nle x:text{$n$ is an $m$-survivor having exactly $k$ prime factors}},$$ where prime factors are counted…
codeforces competitive-programming constructive-algorithms data-structures greedy Jun 11, 2026