"Do not cheat and call your languages' equivalent of str_reverse." Surely calling the use of built-in functions in a programming language "cheating" is somewhat excessive? I find it hard to believe you'd be looking for the kind of candidate that would prefer to invent their own broken-ass string parsing functions instead of relying on standard libraries. I mean I understand what you're getting at, but "Nooooooo! Stop cheating!!!" seems like a pretty poor way to handle your own failure to write proper explicit instructions ;)