[marssaxman]

"Testing" is the wrong attitude. This is not a university exam. You're not trying to determine whether someone has studied the material - that would be a waste of everyone's time.

The point of a useful interview is to learn what it would be like to work with someone. The point of a coding problem is that it gives the candidate a chance to show you how they work. How do they break down a problem and start devising a solution? How do they communicate about their thinking? How do they resolve uncertainty?