Codeforces Alpha Round 21 (Codeforces format)

Solutions for Codeforces Alpha Round 21 (Codeforces format) (contest 21). 3/4 problems verified against sample I/O. Difficulty range: 1900-2400.

4 items

Codeforces Alpha Round 21 (Codeforces format)

Type: Special | Problems: 4 | Verified: 3/4 | Rating range: 1900-2400 | Time: 5m 6s

Problem Name Rating Tags Solve Time Verified
A Jabber ID 1900 implementation, strings 1m 37s ✗
B Intersection 2000 implementation, math 1m 21s ✓
C Stripe 2 2000 binary-search, dp, sortings 1m 26s ✓
D Traveling Graph 2400 bitmasks, graph-matchings, graphs 42s ✓
Practice › Codeforces Solutions › Codeforces Alpha Round 21 (Codeforces format) ›

CF 21A - Jabber ID

We need to validate whether a string follows the exact syntax of a Jabber ID.
codeforces competitive-programming implementation strings May 28, 2026
Practice › Codeforces Solutions › Codeforces Alpha Round 21 (Codeforces format) ›

CF 21B - Intersection

Each input line describes a geometric object in the plane. The equation
codeforces competitive-programming implementation math May 28, 2026
Practice › Codeforces Solutions › Codeforces Alpha Round 21 (Codeforces format) ›

CF 21C - Stripe 2

We are given a stripe consisting of n squares, each containing an integer. The task is to cut this stripe into three contiguous, non-empty segments such that the sum of numbers in each segment is identical. The output is the number of valid ways to perform these cuts.
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Practice › Codeforces Solutions › Codeforces Alpha Round 21 (Codeforces format) ›

CF 21D - Traveling Graph

We are given a weighted undirected graph with up to 15 vertices and up to 2000 edges. Each edge has a positive weight, and there may be multiple edges connecting the same pair of vertices or edges that loop back to the same vertex.
codeforces competitive-programming bitmasks graph-matchings graphs May 28, 2026