AtCoder is a well-known Japanese online programming contest platform that offers real-time judging, strict time limits, and a variety of contest formats. The platform regularly hosts official contests such as ABC, ARC, and AGC, and features a large problem archive, problem categorization, editorials, and ranking systems. It also supports virtual contest (virtual contest) practice.
ABC seriesARC/AGCAPI access, facilitating data analysis and automated practiceWhether you're aiming for the leaderboard, preparing for contests, or doing structured training, AtCoder offers a complete pathway from beginner to expert and a rigorous contest environment.