I have. I had help, but the process was just like any other problem. State constraints. Look for a violation of constraints. Sort of like proof by contradiction

I have. I had help, but the process was just like any other problem. State constraints. Look for a violation of constraints. Sort of like proof by contradiction. I can't remember the actual hints. I blitzed through 3 or 4 naive solutions first. My favorite was using tagged pointers to mark visited nodes. Eventually through a combination of hints and exploration I got to the idea of using two cursors. At that point it was a simple constraint about which cursor would be in front of the other and if there was a violation of that constraint it could only be because of a cycle. It made for a good interview, but there was good chemistry between myself and my interviewer. Any question would have worked in reality.