Not only that, but some worker may be well prepared without even noticing. And without any bad intentions to trick you. This happened to myself (although in a

Not only that, but some worker may be well prepared without even noticing. And without any bad intentions to trick you. This happened to myself (although in a non-interview situation): In general, if you have solved many problems and looked at many solutions, you simply won't remember each specific problem. This effect may start as early as your first math olympiad, and will only get worse on university while you study math and/or computer science. Some time ago I solved a math puzzle, where I got the right ideas relatively quickly, even though I was convinced this problem was new to me. Later I found out in my writings that I actually solved exactly that problem some years ago. Even though I was unable to remember the exact solution, not even remembered I've seen it before, I seem to have internalized enough clues so I could rediscover the exact solution whenever I need it.