Having never heard of a Ring Buffer, based on the interviewer's description I implemented it using a Queue. Doing some post-interview research, I found that the typical implementation uses an array and a couple of indexers for the array. If the interviewer had explained this then I would have implemented accordingly, but I guess to succeed I needed to have known the typical implementation before I came in for the interview. I unapologetically did not recall how to do binary math by hand.