I answered but my code had a couple bugs in it. White-boarding is nerve racking. It's not a good representation of how engineers work throughout the day. Sitting down and doing some pair programming for 15 minutes is a much better idea. Or showing some code samples. It's not fair to the interviewee when the other side has time to prepare their quiz. The most senior engineers can mess up simple white-boarding exercises just because of the anxiety factor. Honestly, I felt like I was back in school taking a test and I've worked in this field for 16 years.