Codeforces Round 685 (Div. 2)

Solutions for Codeforces Round 685 (Div. 2) (contest 1451). 4/7 problems verified against sample I/O. Difficulty range: 800-2700.

7 items

Codeforces Round 685 (Div. 2)

Type: Div. 2 | Problems: 7 | Verified: 4/7 | Rating range: 800-2700 | Time: 16m 10s

Problem Name Rating Tags Solve Time Verified
A Subtract or Divide 800 greedy, math 2m 28s ✗
B Non-Substring Subsequence 900 dp, greedy, implementation 2m 30s ✓
C String Equality 1400 dp, greedy, hashing 1m 22s ✓
D Circle Game 1700 games, geometry, math 1m 5s ✓
E1 Bitwise Queries (Easy Version) 2000 bitmasks, constructive-algorithms, interactive 1m 54s ✗
E2 Bitwise Queries (Hard Version) 2300 bitmasks, constructive-algorithms, interactive 2m 25s ✗
F Nullify The Matrix 2700 constructive-algorithms, games 4m 26s ✓
Practice › Codeforces Solutions › Codeforces Round 685 (Div. 2) ›

CF 1451F - Nullify The Matrix

The problem describes a two-player game played on an $n times m$ matrix of non-negative integers. Players alternate moves, starting with Ashish.
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Practice › Codeforces Solutions › Codeforces Round 685 (Div. 2) ›

CF 1451E2 - Bitwise Queries (Hard Version)

The reported ZeroDivisionError is a symptom, not the root cause. Let's trace the failing input against the code that was previously suggested: The code interprets: - t = 5 - Test 1: a = [2, 4], so n = 2 - Test 2: a = [3, 1], so n = 2 - Test 3: a = [3, 4], so n = 2 - Test 4: a…
codeforces competitive-programming bitmasks constructive-algorithms interactive math Jun 11, 2026
Practice › Codeforces Solutions › Codeforces Round 685 (Div. 2) ›

CF 1451E1 - Bitwise Queries (Easy Version)

We are given a hidden array of size $n$, where $n$ is a power of two. Each element in the array is an integer in the range $[0, n-1]$. The goal is to reconstruct the array by asking at most $n+2$ queries of three types: AND, OR, and XOR between any two indices of the array.
codeforces competitive-programming bitmasks constructive-algorithms interactive math Jun 11, 2026
Practice › Codeforces Solutions › Codeforces Round 685 (Div. 2) ›

CF 1451B - Non-Substring Subsequence

We are given a binary string and multiple range queries. Each query selects a contiguous substring, and we must decide whether this substring can appear as a subsequence somewhere in the same string under a constraint: the subsequence must not be taken as a contiguous block…
codeforces competitive-programming dp greedy implementation strings Jun 11, 2026
Practice › Codeforces Solutions › Codeforces Round 685 (Div. 2) ›

CF 1451A - Subtract or Divide

The reported ZeroDivisionError is a symptom, not the root cause. Let's trace the failing input against the code that was previously suggested: The code interprets: - t = 5 - Test 1: a = [2, 4], so n = 2 - Test 2: a = [3, 1], so n = 2 - Test 3: a = [3, 4], so n = 2 - Test 4: a…
codeforces competitive-programming greedy math Jun 11, 2026
Practice › Codeforces Solutions › Codeforces Round 685 (Div. 2) ›

CF 1451D - Circle Game

We are given a circle centered at the origin with radius $d$. Inside this circle lie all integer lattice points $(x, y)$ such that $x^2 + y^2 le d^2$, but we only care about points in the first quadrant including axes, so $x ge 0, y ge 0$.
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Practice › Codeforces Solutions › Codeforces Round 685 (Div. 2) ›

CF 1451C - String Equality

We are given two strings, a and b, of equal length n, along with an integer k. The goal is to determine whether we can transform a into b using two types of operations. The first operation allows swapping any adjacent characters in a.
codeforces competitive-programming dp greedy hashing implementation strings Jun 11, 2026