I use it as a warm-up in every interview question, and it takes longer to actually write a solution than to reason your way through it, so I've had a long time

I use it as a warm-up in every interview question, and it takes longer to actually write a solution than to reason your way through it, so I've had a long time to think specifically about this problem while waiting for candidates to finish typing. It's always interesting to see what sort of half-baked idea I come up with by the end.