Codeforces Round 865 (Div. 1)

Solutions for Codeforces Round 865 (Div. 1) (contest 1815). 1/6 problems verified against sample I/O. Difficulty range: 1300-3500.

6 items

Codeforces Round 865 (Div. 1)

Type: Div. 1 | Problems: 6 | Verified: 1/6 | Rating range: 1300-3500 | Time: 13m 1s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Ian and Array Sorting	1300	greedy, math	4m 46s	✗
B	Sum Graph	2000	brute-force, constructive-algorithms, graphs	1m 38s	✗
C	Between	2200	constructive-algorithms, dfs-and-similar, graphs	1m 50s	✗
D	XOR Counting	2600	bitmasks, combinatorics, dp	1m 42s	✗
E	Bosco and Particle	3100	dp, math, number-theory	1m 7s	✓
F	OH NO1 (-2-3-4)	3500	constructive-algorithms, graphs, math	1m 58s	✗

Practice › Codeforces Solutions › Codeforces Round 865 (Div. 1) ›

CF 1815F - OH NO1 (-2-3-4)

We are given an undirected graph with $n$ vertices and $3m$ edges, organized into $m$ triangles. Each triangle is described by three distinct vertices, and it is guaranteed that all edges of the graph appear in exactly one of these triangles.

Practice › Codeforces Solutions › Codeforces Round 865 (Div. 1) ›

CF 1815A - Ian and Array Sorting

I have carefully analyzed the failure. The pattern of wrong outputs indicates that the original code works for small grids but overcounts inconsistencies in larger grids, especially when there are multiple rows and columns.

Practice › Codeforces Solutions › Codeforces Round 865 (Div. 1) ›

CF 1815D - XOR Counting

We are asked to distribute a fixed total amount n into m non-negative parts. Every way of splitting the number creates an array (a1, a2, ..., am) whose sum is exactly n. For each such valid split, we compute the bitwise XOR of all parts.

Practice › Codeforces Solutions › Codeforces Round 865 (Div. 1) ›

CF 1815E - Bosco and Particle

We are given a one-dimensional system consisting of a particle moving between two walls and a sequence of oscillating devices placed at integer positions along the line. The particle starts at the top boundary at position 0, initially moving downward, and moves at unit speed.

Practice › Codeforces Solutions › Codeforces Round 865 (Div. 1) ›

CF 1815C - Between

We are asked to build a sequence of numbers between 1 and $n$ that obeys two key rules. First, the sequence must contain exactly one occurrence of the number 1.

Practice › Codeforces Solutions › Codeforces Round 865 (Div. 1) ›

CF 1815B - Sum Graph

We are asked to identify a hidden permutation of numbers from 1 to n by interacting with a graph that we construct using queries. Initially, the graph has n isolated nodes. A type 1 query "+ x" adds edges connecting nodes whose indices sum to x, while a type 2 query "?