No, it's about understanding what an interview is for. They're not trying to get the answer. They're trying to find out what you know, how you think and how you communicate.

Do you spot that it's different with one Vs many plays? Do you spot the binary search? Do you spot that an adversarial opponent can push things? Can you clearly communicate these?

If you just say "I don't know" and that's it you are showing you don't know how to communicate important information and miss soft skills about understanding the context of an interview.

If you say "I don't know" and talk through your thoughts then great. The point is talking things through, even if you have gotten the wrong answer.

Maybe you'd be able to say "and here's how I'd code a simulation to check"