www.topcoder.com is one I've used.
joelt
2010-05-18 18:52:10
+10
A:
Project Euler is the place to go--lots of mathematical problems that have interesting computational solutions.
JSBangs
2010-05-18 18:53:06
Ouch, scooped by 15 seconds while I wrote a little more text. Oh well.
Jefromi
2010-05-18 19:05:41
thank you, it is really good site.
hey
2010-05-19 11:33:27
A:
This question should provide you with a nigh-infinite supply of fun problems.
I also recommend hiring puzzles, such as those from Facebook and ITA.
Kevin L.
2010-05-18 18:57:17
A:
Google CodeJam - There you can find tasks from previous contests
Spoj.Pl - have a lot of ongoing contests and tons of problems
Andrei Taptunov
2010-05-18 18:58:16
+2
A:
http://www.claymath.org/millennium/P_vs_NP/ (they even pay you for solving it). More of them here: http://www.claymath.org/millennium/
jkramer
2010-05-18 19:22:20
A:
I have the USSR Olympiad Problem Book. It is supposed to be solved by brain power (not computer power), but I have found some problems extremely fun to program after I've solved them using pencil and paper.
Many have worked the "Hanoi Tower" problem both in paper and computer, the book I recommend has more similar examples!
Beware: I'm not saying this is a computer related book, I'm just stating that some problems explained therein are fun to program as well.
Cheers,
J.
Arrieta
2010-05-19 00:41:39