[emmett]

(Caveat: I think the existing interview process is fundamentally broken, but because asking people to code on a whiteboard is suboptimal not because the specific questions are wrong)

I've asked this specific question in interviews before, many times.

It's like a slightly harder version of FizzBuzz. It appears to have near perfect discrimination between "knows enough programming to use nested for loops with if-statements" and "does not". Programmers (good or bad), once the given the formal problem statement, solve it in under 20 minutes. People who don't actually really know how to program will never finish.

You might be imagining a slightly more difficult question, but it really is easy. It's an arbitrary coding challenge, sure, but one designed to not be tricky on purpose. The naive implementation works great.