Many years ago, I interviewed a candidate at Amazon for an SDE3 job (aka Senior SDE.) I asked him to write a function that takes 2 sorted arrays of integers and merges them into a single sorted array of integers. He just couldn't do it.

This is very simple problem to solve, and I think anyone who can't do that is not suitable for SDE3 (or 2 or 1, in my opinion)

One could argue about very difficult problems - can a candidate really be expected to invent the solution on the spot, or is it just because they saw it on LeetCode? Is it luck or ability?

But for simple problems, they are a strong negative signal and a very weak positive signal: just because you can merge sorted arrays, doesn't mean you're qualified, but if you can't even do that, you're most likely not qualified.