Judges & Online Resources
My opinionated ranking of different popular judges.
Of course we top the list. Hand-picked problems, an algorithm roadmap, and the Tsuki AI coach, all in one place. Practice right here.
Beginner-friendly contests with some of the cleanest problems in CP. A great place to start.
300 classic problems covering every core topic. A solid standard training set.
Free, topic-ordered guide from Bronze to Platinum with problems and editorials.
Problems organized by algorithm and difficulty for targeted practice.
In-depth CP course and topic list by Shahjalal Shohag. Aimed at more advanced users.
The largest CP community: frequent rounds, editorials, and ratings.
Antti Laaksonen's free Competitive Programmer's Handbook. Read it first.
Huge problem bank, contests, and a strong learning community.
IOI, national, and regional olympiad problems with clean statements.
Large problem archive with structured introductory courses.
Reference problems for testing algorithm-library implementations.
High-level team rounds (Universal Cup). For strong teams.
Host for ICPC, Universal Cup, and other high-level contests.
Reference implementations and explanations for nearly every CP algorithm.
Comprehensive Chinese-language algorithm encyclopedia.
Beginner-heavy problem set, popular in Taiwan.
Indonesian OI (TOKI) contest platform with quality problemsets.
Enormous problem archive (BOJ) with solved.ac difficulty tiers.
Paid interview and competitive practice platform.
Fine for interviews, weak for real competitive programming.
Regular contests and practice; quality varies.
Long-running problem archive; dated UI but many classics.
The classic archive behind Competitive Programming (Halim).
Ural-based archive with many classic algorithmic problems.
Problem archive organized by topic, good for drilling.
Clean problem archive used by many ICPC regionals.
Hosts many Russian and international rounds.
Judge with structured courses and contests.
A free, difficulty-laddered Codeforces problem sheet. Practicing on the judges above tends to serve you better.
Gamified small puzzles; light practice only.
Open-source judge with a broad language set and clean UI.
Basic skill challenges; not useful for serious CP.
A repackaged LeetCode roadmap; interview-focused and dated, not real CP.
Structured paid coaching and the CP-31 problem sheet.
A huge A-to-Z DSA sheet. Comprehensive but grindy; you will get more out of the judges above.