with out knowing what the failing test is

No feedback when printing the input to the console? Then declare a static counter somewhere, update it at each call of your code, and make your solution throw an error just after you printed the critical input. (hopefully, the tests are executed in order...? :s )

seek for an infinite loop.

hint: on cw, the best way to track those is to print some stuff to the console from within each of your loops (something different for each one of them). This way, you'll reach the buffer limit error before the timeout, and you'll be able to identify the loop that is causing trouble.