How often do you get stuck at a problem with no clue about what’s going wrong? You seem to be doing everything right, all the test cases that you’ve thrown at your code pass but still the judge spits out WA. If you are like me, I’d say it happens quite often and it’s very frustrating. If only you could find a failing test case, you could make some progress. In this post, I describe a simple way to find some failing test cases so that you don’t get stuck so easily.