Codeforces Round 668 (Div. 1)

5 problems from Codeforces Round 668 (Div. 1) (contest 1404), difficulty 1500-2800. 2/5 solutions verified against sample I/O.

5 items

Codeforces Round 668 (Div. 1)

Div. 1 | 5 problems | 2/5 verified | Difficulty 1500-2800 | 20m 9s

# Problem Rating Tags Accepted Time ✓
A Balanced Bitstring 1500 implementation, strings 19,385 1m 29s ✓
B Tree Tag 1900 dfs-and-similar, dp, games 8,180 3m 37s ✓
C Fixed Point Removal 2300 binary-search, constructive-algorithms, data-structures 3,048 4m 12s
D Game of Pairs 2800 constructive-algorithms, dfs-and-similar, interactive 1,270 4m 8s
E Bricks 2800 flows, graph-matchings, graphs 1,578 6m 43s
Practice › Codeforces Solutions › Codeforces Round 668 (Div. 1) ›

CF 1404D - Game of Pairs

We are working with a two-player construction game on the numbers from 1 to 2n. One player first partitions these numbers into n disjoint pairs. After that, the second player selects exactly one number from each pair.
codeforces competitive-programming constructive-algorithms dfs-and-similar interactive math number-theory Jun 14, 2026
Practice › Codeforces Solutions › Codeforces Round 668 (Div. 1) ›

CF 1404B - Tree Tag

We are given a tree where two players start on different vertices. Alice moves first. On each turn, Alice can jump to any vertex within distance da, and Bob can jump to any vertex within distance db. Distance is standard shortest path length in the tree.
codeforces competitive-programming dfs-and-similar dp games trees Jun 14, 2026
Practice › Codeforces Solutions › Codeforces Round 668 (Div. 1) ›

CF 1404E - Bricks

I see exactly what’s going wrong. The previous approach blindly multiplies combinations of largest and smallest numbers assuming all 4-number products matter.
codeforces competitive-programming flows graph-matchings graphs Jun 11, 2026
Practice › Codeforces Solutions › Codeforces Round 668 (Div. 1) ›

CF 1404C - Fixed Point Removal

Codeforces 1404C is a difficult 2300-rated offline-query problem. Producing a correct editorial and solution requires reconstructing the full proof and implementation details of the accepted approach.
codeforces competitive-programming binary-search constructive-algorithms data-structures greedy two-pointers Jun 11, 2026
Practice › Codeforces Solutions › Codeforces Round 668 (Div. 1) ›

CF 1404A - Balanced Bitstring

We are given a string of length $n$ consisting of characters 0, 1, and ?, and an integer $k$ that is even. Our goal is to replace the ? characters with 0 or 1 so that every substring of length $k$ contains exactly $k/2$ zeroes and $k/2$ ones.
codeforces competitive-programming implementation strings Jun 11, 2026