13 best websites with Computer Science problems:
E-olymp (e-olymp.com) Ukraine
Codeforces (codeforces.com) Russia
Topcoder (topcoder.com) USA
Codechef (codechef.com) USA
Hackerrank (hackerrank.com) USA
Facebook Hacker Cup (facebook.com/hackercup/) USA
Google Code Jam (code.google.com/codejam) USA
Russian Code Cup (russiancodecup.ru) Russia
acmp.ru Russia
informatics.mccme.ru Russia
CodeCombat (codecombat.com) USA
CodinGame (codingame.com) USA
Empire of Code (empireofcode.com) USA
Джерело: http://it-science.com.ua
