[lewisl9029]

> The point is that this is not a "know it or not" question. You should be able to derive this answer, even if you've never seen it before, by combining things that you should have seen, because they show up all the time in CS.

Sure, you don't absolutely need to know the problem to be able to derive an answer on the spot, but the problem with a widely known question like this is that candidates who already know it will have an almost insurmountable advantage over those who have never heard of it before, which makes it in essence a "know it or not" question.

There is very little you can do to distinguish between the candidates who knew the question beforehand but feigned ignorance versus those who actually managed to figure it out on the spot.

[nostrademons]

That can be pretty easily compensated for by asking the candidate to explain their thinking out loud (which you'd want to do anyway). Someone who's seen it before will be too perfect: they'll just rattle off a solution and it'll be right. Someone who's actively working through it will pause, they'll hesitate, they'll get things wrong and have to correct themselves.

I've occasionally seen candidates who had the answers to interview questions I asked. They actually came clean and said they'd heard it before, but I was already pretty suspicious that they were actively familiar with the question.

[lewisl9029]

> Someone who's actively working through it will pause, they'll hesitate, they'll get things wrong and have to correct themselves.

Candidates who know the solution can and sometimes will do the same. Sure, you can try to catch candidates that try to fake it, but then the process becomes a cat and mouse game between the interviewer and candidate that distracts both parties from the real purpose of the interview, which is to find the most qualified candidate for a position.

None of this would be necessary if the interviewer simply used a lesser known question (or better yet, a more practical question adapted from something taken from the part of the codebase that they'd be working on) to begin with.