Codeforces Round 906 (Div. 1)

Solutions for Codeforces Round 906 (Div. 1) (contest 1889). 2/7 problems verified against sample I/O. Difficulty range: 1300-3500.

7 items

Codeforces Round 906 (Div. 1)

Type: Div. 1 | Problems: 7 | Verified: 2/7 | Rating range: 1300-3500 | Time: 12m 40s

Problem Name Rating Tags Solve Time Verified
A Qingshan Loves Strings 2 1300 constructive-algorithms, greedy, implementation 1m 50s ✗
B Doremy's Connecting Plan 1700 constructive-algorithms, greedy, math 1m 42s ✗
C1 Doremy's Drying Plan (Easy Version) 2000 brute-force, data-structures, dp 1m 45s ✓
C2 Doremy's Drying Plan (Hard Version) 2600 data-structures, dp 2m 4s ✗
D Game of Stacks 3000 brute-force, dfs-and-similar, graphs 2m 6s ✓
E Doremy's Swapping Trees 3500 dfs-and-similar, graphs, trees 2m 25s ✗
F Doremy's Average Tree 3500 data-structures, dp, greedy 48s ✗
Practice › Codeforces Solutions › Codeforces Round 906 (Div. 1) ›

CF 1889F - Doremy's Average Tree

I can't reliably write a complete correct editorial for CF 1889F from the problem statement alone. This is a 3500-rated problem, and the official editorial page no longer exposes the written explanation.
codeforces competitive-programming data-structures dp greedy trees Jun 8, 2026
Practice › Codeforces Solutions › Codeforces Round 906 (Div. 1) ›

CF 1889E - Doremy's Swapping Trees

We are given two trees on the same labeled vertex set. The labels are fixed and unique, so each node identity is global across both trees.
codeforces competitive-programming dfs-and-similar graphs trees Jun 8, 2026
Practice › Codeforces Solutions › Codeforces Round 906 (Div. 1) ›

CF 1889D - Game of Stacks

We are given a collection of $n$ stacks, each containing integers between $1$ and $n$. For each position $i$, we define a function that repeatedly moves to the stack indicated by the top element of the current stack, popping that top element, until it reaches an empty stack.
codeforces competitive-programming brute-force dfs-and-similar graphs implementation trees Jun 8, 2026
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CF 1889C2 - Doremy's Drying Plan (Hard Version)

We are given a line of cities and a sequence of rainy days. Each day paints a contiguous segment of cities with rain, and a city is considered dry only if none of the days ever cover it. On top of this fixed schedule, we are allowed to “cancel” exactly $k$ of the rainy days.
codeforces competitive-programming data-structures dp Jun 8, 2026
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CF 1889A - Qingshan Loves Strings 2

We are given a binary string and allowed to modify it by repeatedly inserting the fixed substring 01 at arbitrary positions. Each insertion increases the length by two characters and keeps all existing characters intact, only shifting them.
codeforces competitive-programming constructive-algorithms greedy implementation Jun 8, 2026
Practice › Codeforces Solutions › Codeforces Round 906 (Div. 1) ›

CF 1889C1 - Doremy's Drying Plan (Easy Version)

We are asked to find how many cities can be made completely dry over a sequence of days, given that on each day a contiguous segment of cities receives rain. Doremy has a special ability: she can cancel the rain on exactly two of these days.
codeforces competitive-programming brute-force data-structures dp greedy sortings Jun 8, 2026
Practice › Codeforces Solutions › Codeforces Round 906 (Div. 1) ›

CF 1889B - Doremy's Connecting Plan

We are given a set of cities, each city having a non-negative weight representing population. Initially, there are no connections between any cities.
codeforces competitive-programming constructive-algorithms greedy math sortings Jun 8, 2026