Just answered an algo interview question in 10m which the interviewer clearly thought would take the whole time. Then he pulled out another question which I ultimately failed to solve and he said "Don't worry I've never seen someone solve it and don't know how"

Little bummed I didn't get the bonus question even though it doesn't matter. Had an easy quadratic solution and I saw a linear one with a ~2^20 overhead but convinced myself a simpler linear solution worked but after writing it realized I was wrong