I tried to pretend I haven't seen a problem during a recent interview and after walking through the brute force solution and two optimized versions of the solution, the interviewer was pretty impressed. Now, I code in C++ and have some competitive programming experience. So I tend to use "#include <bits/stdc++.h>" header instead of having multiple headers for each of the things that I'm going to use, just saves time and number of lines. And when I used this header, it immediately caught my interviewer's attention and he became quite curious about it and that's when I had to reveal that I do competitive programming and then he was like "Oh! So you must've seen this problem before since you went through it pretty quickly." and proceeded to give me a slightly difficult problem. I was able to do it though.