QOJ
Solve and take part in mirrored ICPC regionals and olympiad contests
QOJ is an online judge that hosts a large archive of contests from ICPC regionals, the Universal Cup, Open Cup Grand Prix, national olympiads and Chinese training camps. You can enter live mirror contests, take older ones as virtual contests, or solve their problems one at a time. A Hack feature lets you break other people's accepted solutions with your own tests.
Free · No login · Browser · Advanced
About QOJ
It trains contest-level algorithms and data structures and suits advanced competitive programmers who want fresh, hard problem sets soon after the official events.
It runs in the browser, and you can browse problems without an account but need one to submit. The interface is in English, and many contest titles are in Chinese.
On Breakpoint since 25 Oct 2026.
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