It’s a great site and greatly accelerated my learning of programming.

The form of learning which I call “problem based” learning is a great format for me. You learn from reading up on a topic. You learn from trying different solutions. Finally, you learn from seeing other people’s answers once you’ve solved it.

Also check out:

Hackerrank.com - all around focus Project Euler- math focus Leetcode - more oriented towards interview training but still useful and fun.