The one thing interviewers need to stay aware of though is that they will have immense insight into the problem whereas the candidate likely has never thought through the problem space before. And this can lead to unfair judgements. I know I've fallen into this trap before, where I'd run the same session with so many candidates that I had a thorough big picture view of every possible approach. I'd see a candidate stumbling a bit and think, "Why can't they see the obvious answer in front of them?" when in fact I wouldn't have seen it on my first go either. I just had seen dozens of candidates go through the same exercise to the point where it seemed like old hat.
The one thing interviewers need to stay aware of though is that they will have immense insight into the problem whereas the candidate likely has never thought through the problem space before. And this can lead to unfair judgements. I know I've fallen into this trap before, where I'd run the same session with so many candidates that I had a thorough big picture view of every possible approach. I'd see a candidate stumbling a bit and think, "Why can't they see the obvious answer in front of them?" when in fact I wouldn't have seen it on my first go either. I just had seen dozens of candidates go through the same exercise to the point where it seemed like old hat.