Codebreaker (Singapore)
Train on olympiad problems from the judge Singapore uses to pick its IOI team
Codebreaker is the official training and contest platform for the Singapore Informatics Olympiad. It has run IOI team selection for Singapore and Indonesia, and its problem archive holds over 2,300 olympiad-style tasks graded by an online judge.
Free · Browser · Intermediate
About Codebreaker (Singapore)
Beyond the archive you can browse newest, unsolved and recommended problems, join public contests, take timed practice sets and work through collections. Schools also run training contests on it, with several scheduled for early November 2026. It suits secondary-school and university students preparing for olympiads, and anyone who wants IOI-style practice with partial scoring.
The site is in English, runs in the browser, and is funded by donations. It has users from more than 100 countries and nearly a million submissions.
On Breakpoint since 31 Oct 2026.
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