Codeforces Round 864 (Div. 2)

Solutions for Codeforces Round 864 (Div. 2) (contest 1797). 2/6 problems verified against sample I/O. Difficulty range: 800-3000.

6 items

Codeforces Round 864 (Div. 2)

Type: Div. 2 | Problems: 6 | Verified: 2/6 | Rating range: 800-3000 | Time: 10m 17s

Problem Name Rating Tags Solve Time Verified
A Li Hua and Maze 800 constructive-algorithms, flows, graphs 1m 35s ✗
B Li Hua and Pattern 1100 constructive-algorithms, greedy 1m 21s ✓
C Li Hua and Chess 1600 constructive-algorithms, greedy, interactive 1m 47s ✗
D Li Hua and Tree 1900 brute-force, data-structures, dfs-and-similar 2m 3s ✓
E Li Hua and Array 2300 brute-force, data-structures, dsu 1m 54s ✗
F Li Hua and Path 3000 data-structures, dfs-and-similar, divide-and-conquer 1m 37s ✗
Practice › Codeforces Solutions › Codeforces Round 864 (Div. 2) ›

CF 1797E - Li Hua and Array

We are given an array of integers and two types of operations. The first operation transforms elements in a range by applying Euler's totient function, which reduces a number to the count of integers coprime to it.
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Practice › Codeforces Solutions › Codeforces Round 864 (Div. 2) ›

CF 1797F - Li Hua and Path

We are working with a rooted but otherwise unrooted tree where every vertex carries a unique label from 1 to n, and these labels matter structurally rather than just as identifiers. For any two vertices u and v, consider the unique simple path connecting them.
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CF 1797D - Li Hua and Tree

We are given a rooted tree with n vertices, where each vertex has a numerical importance. The root is vertex 1. Two types of operations can be performed on this tree. The first operation asks for the sum of importance values in the subtree rooted at a given node.
codeforces competitive-programming brute-force data-structures dfs-and-similar dp implementation trees Jun 9, 2026
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CF 1797C - Li Hua and Chess

We are dealing with a hidden position on an extremely large grid, up to one billion in both dimensions. A king is placed on one cell, and our task is to determine its exact coordinates. We cannot directly access the position.
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Practice › Codeforces Solutions › Codeforces Round 864 (Div. 2) ›

CF 1797A - Li Hua and Maze

This is a Type B (prove) problem: the task is to prove that the intersection point of the diagonals of quadrilateral $ABCD$ coincides with the intersection of the common internal tangents of the two circles. The solution correctly addresses a proof,
codeforces competitive-programming constructive-algorithms flows graphs greedy implementation Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 864 (Div. 2) ›

CF 1797B - Li Hua and Pattern

We are given an $n times n$ grid where each cell is either 0 or 1, representing two colors. We are also given a fixed number $k$ of moves. A single move flips the color of exactly one chosen cell.
codeforces competitive-programming constructive-algorithms greedy Jun 9, 2026