Code Katas

Code katas:
http://www.codekatas.org/
http://www.codingdojo.org/cgi-bin/index.pl?KataCatalogue
http://codekata.com/
https://laracasts.com/series/code-katas-in-php
http://en.wikipedia.org/wiki/Kata_(programming)

Also see
how to get job in facebook
Code problems:
http://www.careercup.com/page