Should you tell the interviewer that you have heard the question before no matter how many questions are repeated?

This actually happened to me when I was recruiting at IIT Bombay for an analyst position at McKinsey. This was a coveted position with several applicants vying for very few positions. All the candidates were seated in a large classroom on campus and each of us had multiple rounds with short breaks in between. 2 of my friends were sitting in front of me and were discussing one of their prior interviews where they had been asked to estimate the weight of an aircraft. When I went in to my interview with one of the senior partners, he asked me to estimate the weight of an aircraft and I told him that I had just heard someone else discussing the same problem and that he should ask me something else. He was a little surprised but decided to ask me a twist on the same question - he gave me a weight and asked me whether that seemed reasonable. 6 year's later I'm back at McKinsey and I do not think I would be here if I hadn't been honest on that first interview day.

It depends on the type of question, and frankly if I am interviewing you and you said you had heard the question, I'd love it. It shows me you have done a lot of reading on the subject matter. However as I said, it depends on the question. Usually I start the interview with a basic question such as the fibonacci number, I know that most of the people who come there know the answer to it, and it is just a question to get the ball rolling. These type of questions, it would be better off if you answered it, rather than telling me you know the answer to it or if you have come across it, but if you did, no issues. After you answer this question, I'd either try to complicate the question of fibonacci numbers a bit more or I would ask another question on recursion. Another type of question, that I usually ask is knowledge based or design related questions. You should just answer the question for this, I am actually testing whether you know it or not. I'd like to hear the answer to these type of questions even if you know them or have come across them, especially design related questions because there is no one answer to it. To summarise, I love the upfront honesty of the person who says he came across the question, but there are some easy questions or knowledge/design related questions which you should answer over telling that you know it.

Humbly, "I've already heard this one before. Can we do another?" Will take you further than a flawless, artificially rehearsed answer.

Yes. At least that way you make sure the question you remember is the *same* as the one you're being asked. I assume anyone who's been doing a lot of interviewing will have heard many common questions.

Of course. If you can't be honest with your (hopefully) future coworker, do you really want to work there? For example, I interviewed for a job a while back and the fizz-buzz exercise was one of the questions. I had heard of it and solved it in several languages the previous week. I told them my experience with the problem and they immediately moved to a more intermediate problem which I actually enjoyed talking through both recursively and with looping. I got the job and am loving it. What the interviewer is looking for (or should be looking for) is how you think through a problem as you're solving it for the first time. Because those are the challenges that they need you to be able to solve on the job every day. If you don't tell them that you know the problem and you get the job but can't solve the day-to-day challenges, then you won't last long. If you can step up and solve their day-to-day problems, then you should be able to answer the interview questions well enough for them to hire you. (I've worked primarily for smaller companies. I have no clue how hiring/programming works at larger companies.)

Honestly, I don't get why it should matter if you've already seen the problem. They've asked you to solve a problem and you solve it. As long as you aren't breaking any laws, does it matter how you got there? If you write an exam and you've seen one of the exam questions before--from practice problems, or an old exam or whatever--does that mean you should get docked marks? It suggests you were prepared. Maybe in your previous job you had to solve similar problems all day long, thus proving that you have experience. This is usually the most efficient way to solve problems: find another problem that's equivalent. If I need to solve a matrix, I don't sit around and re-derive Gaussian elimination, I just use one of the canned solvers which is probably a lot more numerically stable. If you know the solution already that's the most efficient way to get there and isn't efficiency what today's employers are looking for above all else? Stuff like this informs my why I am so cynical of the entire job hunting process.

Yes. It happened to me a few times and I always told them that the question was the same or similar to a question that another interviewer had just asked me. The most important reason is because I want to be judged on my technical skills and abilities and I feel confident that I'm a strong developer. If I'm not good enough or not the right fit for a company then that's fine. Another reason is because interviewers will compare notes with each other in order to decide if you're a good fit. If I knew that a recruit had answered the same question twice I would think that they didn't have good ethics or that their technical skill wasn strong enough to recognize that the same solution would apply in both questions. In either case I wouldn't recommend that candidate for the position. Good luck!

Yes, you should tell the interviewer only if: The interviewer has asked about it. You can write the complete solution without any errors and without thinking about the solution at all. It'd look really bad if you claim to know the solution and then have a hard time solving it. While preparing for interviews, you'll have heard about a lot of questions. So, about half the time, you'll have heard the question in some form. If you've just heard the question and don't know the solution, just say no to avoid any confusion. Be honest, either way. If you know the solution, just write it while making sure it's bug free. Don't  fake it.

Some employers intentionally ask basic/common questions because (1) they want to see how well you prepare and how many common problems you have solved; (2) they want to see you can really solve it, not just saying that you know it; (3) they have their own further questions that based on some common problems; (4) they want to see how well you can explain your answers, which I think is the most important of all. If you can't explain well, you may have trouble sharing ideas in a team, which is a big no-no. I agree with Ash Moorthy. If they ask whether you have seen it elsewhere, you tell the truth. Otherwise, just answer their questions. If you do well in the basic questions, they may have some more advanced questions for you.