Bumped into this web site:



http://codility.com



It's a web site where they test coders, and every so often, they offer a public challenge you can use to hone your algorithm-design and coding skills.



These are great brain-teasers, and I had tremendous fun solving the challenges - I did the last one of 2013 and the new one of 2014 that was just released.




And I managed to get some badges!


Codility badge



Codility badge




Warning: the challenges are not trivial, and it's one of those 'cannot let it go' things: once you click 'Challenge yourself', you'll find yourself hooked!