I used to ask this (cycles in linked list) question all the time, and I found it useful as a way to see how the candidate worked through an unfamiliar problem.

I used to ask this (cycles in linked list) question all the time, and I found it useful as a way to see how the candidate worked through an unfamiliar problem. No-one gave the 2-pointer answer, ever. For me it wasn’t a pass/fail “do you know the right answer” question, it’s more of a “can I work with this person” question.