Comment by singron

It probably wasn't the situation in your case, but I often give straightforward hints if the candidate is struggling with something that I don't want them to spend time on so we can get to the significant material.

E.g. in an algorithms interview they get stuck on an unrelated python issue (many people interview in python but don't use it day to day), or in a system design interview they get stuck on designing extra-credit subsystem C when they haven't finished subsystems A and B.

If they aren't getting it after a couple hints, I'll just tell them the answer or tell them to come back to it later.

Anyway, I would be very careful if you aren't going where the interviewer is pointing you. If you think it's a trick or you want to practice Active Ethics, then I would call that out in the moment since you might be messing up the flow of the interview at best and come off as hard to work with at worst.