Resources
Useful sites and books for CCC preparation.
Online judges and tutorials
DMOJ
A modern online judge with an extensive problem library, including every CCC contest.
Codeforces
One of the most popular competitive programming platforms — regular contests and a huge problem archive sorted by difficulty.
AtCoder
Japanese contest platform known for clean, well-tested problems and beginner-friendly contests every weekend.
CSES Problem Set
by Antti Laaksonen
200+ classical problems covering sorting, graphs, DP, and more. Pairs perfectly with the Competitive Programmer's Handbook.
USACO Guide
Comprehensive USACO prep guide with harder problems and editorials, mostly targeted at C++ users.
CP-Algorithms
Encyclopedic reference for competitive programming algorithms with explanations, code, and complexity analysis for almost every standard technique.