Wikipedia
Codeforces
Codeforces is a Russian website dedicated to competitive programming. It was created and is maintained by a group of competitive programmers from Saratov State University led by Mikhail Mirzayanov. Since 2013, Codeforces has surpassed TopCoder in terms of active contestants 12. Codeforces Round #365 (Div. 2) contest broke all records in terms of registrants: 73123.