Indeed. Most probably OT, but this reminded me of the appendix Secrets of Programmer Jobs Interviews from a book I enjoyed reading a couple of years ago: Expert C Programming - Deep C Secrets (with a fish on the cover ;-) by Peter van der Linden (1994) (Update: search http://books.google.com/).

The task is to detect a loop in a linear list. First you are allowed to sketch any algorithm you like. Then more and more restrictions are imposed like the list is read-only, RAM is too limited, must use CPU registers only, etc.