Codeforces Round 663 (Div. 2)

5 problems from Codeforces Round 663 (Div. 2) (contest 1391), difficulty 800-2600. 3/5 solutions verified against sample I/O.

5 items

Codeforces Round 663 (Div. 2)

Div. 2 | 5 problems | 3/5 verified | Difficulty 800-2600 | 17m 2s

# Problem Rating Tags Accepted Time ✓
A Suborrays 800 constructive-algorithms, math 25,062 4m 35s
B Fix You 800 brute-force, greedy, implementation 29,778 55s ✓
C Cyclic Permutations 1500 combinatorics, dp, graphs 16,025 1m 29s ✓
D 505 2000 bitmasks, brute-force, constructive-algorithms 5,762 7m 33s ✓
E Pairs of Pairs 2600 constructive-algorithms, dfs-and-similar, graphs 1,926 2m 30s
Practice › Codeforces Solutions › Codeforces Round 663 (Div. 2) ›

CF 1391B - Fix You

The grid describes a deterministic system where every cell contains exactly one outgoing instruction: either it sends any item to the right or it sends it downward.
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Practice › Codeforces Solutions › Codeforces Round 663 (Div. 2) ›

CF 1391D - 505

We are given a binary grid and we are allowed to flip cells from 0 to 1 or 1 to 0. The goal is to transform the grid so that every square submatrix whose side length is even contains an odd number of ones.
codeforces competitive-programming bitmasks brute-force constructive-algorithms dp greedy implementation Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 663 (Div. 2) ›

CF 1391A - Suborrays

We are asked to construct a permutation of the numbers from 1 to n such that every contiguous segment behaves in a very specific way under the bitwise OR operation. For any subarray, we take all values inside it and compute their bitwise OR.
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Practice › Codeforces Solutions › Codeforces Round 663 (Div. 2) ›

CF 1391E - Pairs of Pairs

We are given a connected undirected graph, and the task is not to compute a classical graph property, but to construct one of two global structures that are guaranteed to exist. The first possible output is a simple path that visits at least half of the vertices.
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Practice › Codeforces Solutions › Codeforces Round 663 (Div. 2) ›

CF 1391C - Cyclic Permutations

We are given a permutation of numbers 1...n. From that permutation, a graph is constructed on the indices of the array. For every position i, we connect it to the nearest larger element on the left and the nearest larger element on the right, whenever such elements exist.
codeforces competitive-programming combinatorics dp graphs math Jun 11, 2026