I did this once! I was given a "create Battleship" take-home assignment. Normally, I'd say, "yeah, I don't have time for this". But I happen to really like that game and had never thought of how to model it in code. So I took up the challenge. I spent time whiteboarding classes, interfaces, writing tests... in the end, I had a solid solution. I submitted my code and as I was doing so, I thought, "you know, this really could be handled by a couple of Set data structures. After hitting send, I did a quick follow-up with, "you know, this has a very simple solution" and typed some example code right in the body of the email. I love it when I can't just leave a problem alone. The hiring manager appreciated it too!