Codeforces Round 838 (Div. 2)

Solutions for Codeforces Round 838 (Div. 2) (contest 1762). 2/7 problems verified against sample I/O. Difficulty range: 800-3100.

7 items

Codeforces Round 838 (Div. 2)

Type: Div. 2 | Problems: 7 | Verified: 2/7 | Rating range: 800-3100 | Time: 32m 22s

Problem Name Rating Tags Solve Time Verified
A Divide and Conquer 800 greedy, math, number-theory 2m 14s ✓
B Make Array Good 1100 constructive-algorithms, implementation, number-theory 3m 4s ✗
C Binary Strings are Fun 1400 combinatorics, math 10m 29s ✓
D GCD Queries 2100 constructive-algorithms, interactive, number-theory 2m 21s ✗
E Tree Sum 2600 combinatorics, math, trees 4m 2s ✗
F Good Pairs 2600 binary-search, data-structures, dp 3m 10s ✗
G Unequal Adjacent Elements 3100 constructive-algorithms, sortings 7m 2s ✗
Practice › Codeforces Solutions › Codeforces Round 838 (Div. 2) ›

CF 1762G - Unequal Adjacent Elements

We are given an array of values and asked to reorder indices, not values, into a permutation. The permutation must satisfy two simultaneous constraints. First, every element from the third position onward must be strictly larger than the element two positions before it.
codeforces competitive-programming constructive-algorithms sortings Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 838 (Div. 2) ›

CF 1762C - Binary Strings are Fun

We are given a binary string s. For every prefix of s, we define a value f(prefix). To compute f(x), we look at all possible extensions of x. If x has length k, an extension has length 2k-1.
codeforces competitive-programming combinatorics math Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 838 (Div. 2) ›

CF 1762F - Good Pairs

We are asked to count the number of "good pairs" in an array. A pair of positions $(l, r)$ is good if we can move from index $l$ to $r$ by hopping forward in the array along a sequence of indices where each consecutive pair differs by at most $k$.
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Practice › Codeforces Solutions › Codeforces Round 838 (Div. 2) ›

CF 1762E - Tree Sum

We are asked to consider edge-weighted trees with vertices numbered from 1 to $n$, where each edge has weight either $1$ or $-1$. A tree is called good if for every vertex, the product of the weights of all edges incident to that vertex equals $-1$.
codeforces competitive-programming combinatorics math trees Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 838 (Div. 2) ›

CF 1762D - GCD Queries

We are asked to find an index of the element 0 in a hidden permutation of integers from 0 to n-1. The permutation is not given directly, but we can ask for the greatest common divisor (GCD) of any two distinct elements in the array.
codeforces competitive-programming constructive-algorithms interactive number-theory Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 838 (Div. 2) ›

CF 1762B - Make Array Good

We are asked to transform an array of positive integers into one that is "good" according to a divisibility property: for every pair of elements, the larger must be divisible by the smaller.
codeforces competitive-programming constructive-algorithms implementation number-theory sortings Jun 9, 2026
Practice › Codeforces Solutions › Codeforces Round 838 (Div. 2) ›

CF 1762A - Divide and Conquer

We are given an array of positive integers and we are asked to make its sum even using a special operation: pick any element and replace it with its integer half, the floor of dividing by two.
codeforces competitive-programming greedy math number-theory Jun 9, 2026