Educational Codeforces Round 138 (Rated for Div. 2)

Solutions for Educational Codeforces Round 138 (Rated for Div. 2) (contest 1749). 2/6 problems verified against sample I/O. Difficulty range: 800-2800.

6 items

Educational Codeforces Round 138 (Rated for Div. 2)

Type: Div. 2 | Problems: 6 | Verified: 2/6 | Rating range: 800-2800 | Time: 24m 42s

Problem Name Rating Tags Solve Time Verified
A Cowardly Rooks 800 greedy, implementation 5m 44s ✗
B Death's Blessing 900 greedy 2m 33s ✗
C Number Game 1400 binary-search, data-structures, games 2m 10s ✗
D Counting Arrays 1900 combinatorics, dp, math 2m 47s ✓
E Cactus Wall 2400 constructive-algorithms, dfs-and-similar, graphs 9m 15s ✗
F Distance to the Path 2800 data-structures, dfs-and-similar, trees 2m 13s ✓
Practice › Codeforces Solutions › Educational Codeforces Round 138 (Rated for Div. 2) ›

CF 1749E - Cactus Wall

The problem presents a rectangular grid representing a sand field in which some cells already have cacti. Cacti cannot be adjacent to each other horizontally or vertically.
codeforces competitive-programming constructive-algorithms dfs-and-similar graphs shortest-paths Jun 9, 2026
Practice › Codeforces Solutions › Educational Codeforces Round 138 (Rated for Div. 2) ›

CF 1749F - Distance to the Path

We are given a tree with $n$ vertices. Each vertex initially holds a value of zero. There are two kinds of queries. The first type asks for the current value of a specific vertex.
codeforces competitive-programming data-structures dfs-and-similar trees Jun 9, 2026
Practice › Codeforces Solutions › Educational Codeforces Round 138 (Rated for Div. 2) ›

CF 1749A - Cowardly Rooks

Ah, now I see the real issue. The previous solution overgenerates operations. It blindly flips every 1 in a individually and then applies parity-fixing operations.
codeforces competitive-programming greedy implementation Jun 9, 2026
Practice › Codeforces Solutions › Educational Codeforces Round 138 (Rated for Div. 2) ›

CF 1749D - Counting Arrays

We are asked to count arrays of length up to $n$ with values between $1$ and $m$ where there exists more than one valid removal sequence.
codeforces competitive-programming combinatorics dp math number-theory Jun 9, 2026
Practice › Codeforces Solutions › Educational Codeforces Round 138 (Rated for Div. 2) ›

CF 1749B - Death's Blessing

We are asked to determine the asymptotic value of the probability that $k+1$ consecutive bits generated by $$Yn = (Y{n-1} + Y{n-2}) bmod 2$$ contain more 1s than 0s, under the conditions that $k 2l$ and the period length of this recurrence is $2^l - 1$, for large $k$.
codeforces competitive-programming greedy Jun 9, 2026
Practice › Codeforces Solutions › Educational Codeforces Round 138 (Rated for Div. 2) ›

CF 1749C - Number Game

We are asked to analyze a two-player game played on an array of positive integers. Alice chooses a number of stages $k$ she wants to play, and in each stage she must remove an element from the array that is at most the number of the remaining stage.
codeforces competitive-programming binary-search data-structures games greedy implementation Jun 9, 2026