The interviewer asked me a medium level leetcode question, and I solved that in 10 minutes. Instead of him to ask a second question, he kept asking to optimise to O(1), which was more mathematical than logical. When the feedback came, he failed me because "I spent so much time on the first question and didn't attempt the second". Dude, if there was a second question, why did you ask me to come up with a mathematical approach for an O(1) traversal of a 2D grid.