Halite.io!

A fun social platform for hackers to solve interesting puzzles, build quick hacks, code game bots and collaborate to solve real-world challenges.

Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.

CodinGame is a challenge-based training platform for programmers where you can play with the hottest programming topics.

Develop your coding skills and practice them by competing with hundreds of players worldwide. Code your own bots in your preferred language and join the various competitions that we offer. Learn, win prizes, but most importantly, have fun coding! Check out the our current competitions to see how you could get started.

SPOJ (Sphere Online Judge) is an online judge system with over 315,000 registered users and over 20000 problems. The solution to problems can be submitted in over 60 languages including C, C++, Java, Python, C#, Go, Haskell, Ocaml, and F#. SPOJ has a rapidly growing problem set/tasks available for practice 24 hours/day, including many original tasks prepared by the community of expert problem setters associated with the project.

Built by CodeFights, Code Arcade challenges players to solve programming tasks to complete game levels. It's a fun way to hone coding skills.