This is indeed an excellent idea for an interview. (By far my favorite hour of interviewing the last time around was the Stripe "debugging" interview, which is

This is indeed an excellent idea for an interview. (By far my favorite hour of interviewing the last time around was the Stripe "debugging" interview, which is quite similar to this.) But maybe they will still use chatgpt to help them figure out the solution. A non-trivial number of my interactions with it are of this form, "no, that isn't right, fix this part and re-do the rest". And that should be fine. Or it should be fine to not do it that way. The goal is to get a sense for how the person you may or may not be working with approaches solving problems. Sometimes LLMs are part of how they do that, sometimes they aren't. And you can learn something about them from that, either way.