This is what everybody who employs a vanity interview question tells themselves. You can use this logic to justify any question, and the result is an entirely subjective interview process that occasionally and randomly admits candidates based on their knowledge of trivia.

How do you differentiate between:

1. Someone genuinely solving the question on the fly

2. Someone who memorized the answer, and is just pretending to solve it on the fly

That's an interesting observation. So what you are saying is that if I make sufficient headway into the problem without providing the most efficient answer, it should be fine?

There are rumors that unless you are spot on perfect in Big 4 interviews, they wont advance you.

I mean, aren't those algorithms developed by CS professors/researchers/Ph.D's/mathematicians? As a junior developer I seriously doubt I'd even approach the problem the same way as the super smart person who developed that algorithm.

Ditto.