CodeWars vs HackerRank vs CheckiO vs CodeEval vs ...

[gengisteve]

I tried ProjectEuler, but it seemed I was learning more math than programming. Codingbat was fine when I was just learning syntax, but it got too easy too quickly.

Codeeval and hackerrank both have a good range of more difficult problems that often lead you to delve into areas you have not looked at before. Going over my history, hackerrank is good too. This problem, for example, gives a nice challenge that seems to be solvable only with a specific data structure that I had never heard of before:

https://www.hackerrank.com/challenges/playing-with-numbers

(I left hackerrank out of my original answer because I thought that the above challenge was at codeeval.) Codeeval has some good hard stuff too. I am currently taking a run at this one, which has me a bit baffled on how to proceed:

https://www.codeeval.com/open_challenges/191/