I was asked to map a mathematical problem to an algorithm for first round of interview. I did it in 5 lines with O(n) and it worked. was told that was not the correct answer sent me an answer with O(n^2) and about 40 lines. in anger, I sent a five page mathematical proof along with analysis why mine was better. surprisingly, they took me in for second round. tanked it because I continually stuttered and froze. I was able to answer it once I got home. decided against sending it.