I've had similar experience - in an interview for my current job I got asked same question that I've already encountered in a previous job interview. It must be

I've had similar experience - in an interview for my current job I got asked same question that I've already encountered in a previous job interview. It must be pretty popular in the area :) It wasn't hard, and I solved it first time without help so it didn't feel like cheating, but I told the guy afterwards anyway. I did tech interviews from the other side before and from my experience having the perfect answer doesn't matter that much - what matters is showing how you solve problems and that you're familiar with common solutions and trade-offs.