COCI (Croatian Open Competition in Informatics)
Solve five olympiad tasks in three hours in a monthly online contest open to everyone
COCI is an online contest series run each school year by Croatia's informatics competition organisers. Each season has five contests, roughly one a month from October to February; each lasts three hours and has five olympiad-style tasks with full feedback and up to 50 submissions per task.
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About COCI (Croatian Open Competition in Informatics)
Tasks range from beginner-friendly to hard, so it works both for students preparing for national olympiads and for experienced competitive programmers who want a regular IOI-style round. Tasks, test data and solutions from every season back to 2006/2007 are published in the archive.
Anyone may enter. Contests run on evaluator.hsin.hr, which needs an account, and accept Python, Pascal, C/C++ and Java. The 2026/2027 season started on 24 October 2026; the next rounds are 14 November and 12 December 2026, 23 January and 20 February 2027.
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