AtCoder 2026-01-30
Saw this one mentioned on some Project Euler forum threads.
Kaggle Updated 2026-01-30
To be fair, this is one of the least worse ones.
LeetCode Updated 2025-07-16
Their system is quite good actually. Not as good as a GitHub repo with all the tests made explicit. But still pretty good.
Exercism Created 2025-03-20 Updated 2025-07-16
SPOJ 2026-01-30
Submission type: code.
License: problem setter dependant.
UVa Online Judge Created 2025-03-20 Updated 2026-01-30
License: problem setter dependant, they appear to collect from past competitions.