[jillav]

I don't mind those questions in an interview as long as the recruiter is not just reading them from a paper sheet, and actually know this stuff. This can be a way to find a candidate with a strong theorical CS background. Which can be relevant for some positions.

Now, I've seen my fair share of recruiters that did not really understand the topic at hand when asking theorical CS questions, let alone the desired answer. I do so always get really suspicious when they occur.