[QuercusMax]

And if the candidate trips up, this gives you an opportunity to walk through a virtual compile-debug-test cycle.

When I asked these kinds of questions I would execute the program in my head, and tell the candidate things like "your reverse() methods moves some stuff around, but the end result appears the same as before". Or "this fails with ArrayIndexOutOfBounds on line X". Typically it only took a few minutes to find the bug and fix it, and I learned about how the candidate solves problems.