If you like this kind of thing and have a slightly competitive mindset, you might also like: http://www.codeforces.com http://www.codeforces.com http://www.top

If you like this kind of thing and have a slightly competitive mindset, you might also like: http://www.codeforces.com http://www.codeforces.com http://www.topcoder.com/tc http://www.topcoder.com/tc