I often use Advent of Code. Previous years that I haven't solved. They are smallish, self-contained problems with solutions provided. It also gives me questions

I often use Advent of Code. Previous years that I haven't solved. They are smallish, self-contained problems with solutions provided. It also gives me questions that I don't have a predetermined solution for. I read through the problem with the interviewee, we collaborate on a high-level solution, and then I let them implement. It's as close as I can get to modeling how I would work with someone while still being in an interview context.