AtCoder
Join timed algorithm and heuristic contests from Japan
AtCoder is a Japanese contest site. You join timed contests, solve algorithm problems and submit code that is judged right away. Contest types include the Beginner Contest (ABC), Regular Contest (ARC) and Grand Contest (AGC). There is also a Heuristic Contest (AHC), where you find the best answer you can to an optimization problem.
Free · Browser · Intermediate
About AtCoder
It trains algorithm skills and clean, correct code. Each contest sets which rating range is rated, so the ABC suits newer players and the AGC suits the strongest. You get separate ratings for algorithm and heuristic contests.
Contests run often, many on weekends. You need an account to take part, and the site suggests a practice contest for first-time users.
On Breakpoint since 23 Oct 2026.