[roganartu]

When you’re an interviewer and you’ve asked the same question enough (tens of time is plenty, really) you’ve seen it all and it’s really obvious when someone has seen the question before.

People who haven’t seen the question before always stumble somewhere. There’s something they didn’t notice at first and need to account for, their solution is not structured optimally for the follow ups, they iterate over some possible solutions while thinking out loud to eliminate them etc.

It’s honestly not that hard to tell when someone is pretending they haven’t seen it before.

[naiwenwt]

As an interviewer I find it easy to catch candidates who are regurgitating a memorized answer, but catching people who know the answer in-and-out is really hard. I've had the exact same experiences on the interviewing side of the table as well.

I think interviewers tend to overestimate their ability to catch people who have seen the question before and miss on tons of candidates who are good at answering seen questions.

[saagarjha]

It's actually not all that hard to stumble on the question at predictable spots. My process for solving a question I've seen before and one that is new to me actually doesn't differ all that much: as several clarifying questions at the start to confirm I understand the problem, then write a quick-n'-dirty solution as fast as possible. In this first pass I usually don't pay too much attention to things like bounds, which you wouldn't memorize anyways even if you knew the solution. Then I run a pass to polish the solution up, present it, then think of edge cases and how I'd test the solution. The only real difference is that I very rarely pretend not to have seen a question (I have done it twice, both in situations where it was clear the interviewer was out of questions and running down a list of things from memory, and I just wanted to humor them). You'd think that I'd be more sure of myself when I actually know the answer, but when I don't actually know what I'm doing I will usually come to the answer as I ask those clarifying questions and start stating the facts that usually score "this person at least has the gist of the problem" points, like "oh this is a graph and we're doing something with distance, let's see if Dijkstra is the right thing to apply".