The exact same number of times I've been asked that during an interview: 0!
I do ask tree traversal questions when interviewing because I've had to traverse a lot of trees so I think being able to do an in order traversal of an already sorted binary tree (which is only a handful of lines of code) is fair game.
I do ask tree traversal questions when interviewing because I've had to traverse a lot of trees so I think being able to do an in order traversal of an already sorted binary tree (which is only a handful of lines of code) is fair game.