Same, in an interview a few months I got a graph one which I did OK in. Then I got asked to write an algorithm to determine if it is acyclic on not. I could remember the visitation flag but I could not remember, of the top of my head, which side of the recursive call it was on. I picked the later side and obviously failed as I didn't get any offer, although that was more likely due to my age. I dodged a bullet in the end.