Spoj - Sphere Online Judge created for the coders' community to train, to learn and to make progress.

Codingbat - The online programming practice in java and python.

LeetCode - Practice and level up your development skills and prepare for technical interviews.

The AI Games - Challenge people worldwide by coding bots in awesome games.

Rosetta Code - Rosetta Code is a programming resource that provides example problems of how to write the same...

HackerRank - HackerRank is a platform that allows companies to conduct interviews remotely to hire developers and for technical assessment purposes.