[ puzzles to try ]
http://blogs.lessthandot.com/index.php/ITProfessionals/EthicsIT/collection-of-puzzles-for-programmers

Become a better programmer with programming challenges
http://macgyverdev.blogspot.se/2014/04/become-better-programmer-with.html
http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=3