If you find that a useful learning experience, you may want to try http://projecteuler.net/ http://projecteuler.net/ I've thought "How can my solution possible

If you find that a useful learning experience, you may want to try http://projecteuler.net/ http://projecteuler.net/ I've thought "How can my solution possible be wrong" numerous times while doing those problems. Makes you realize how often mistakes slip through in real code, 'that can't possibly be wrong'. Even when you have tests, because for complex behavior, your test case solution may easily be wrong (or worse: derived from your algorithm... I'm guilty of that mistake)