My favorite programming question to ask is: Write a function that given an integer n returns the number 1 to n in random order

I find this is a good mix of not too trivial but not overwhelming, I don't expect people to come up with the fastest possible algorithm on the spot. If they code the naive solution, that's OK if it makes sense and they can describe the performance characteristics. Then we'll talk over the algorithm and I lead them to something better and see how the conversation develops.