I'm not sure what to make of the fact that for the abstract matrix problem in the original post, I thought about it for a moment without making any progress, but then for the knights on the phone pad problem it took me just two moments (about twenty seconds) to come up with the third solution -- and for context, I'm a product manager with a history as a developer. It would take me less than five minutes to code it up.

I wish I hadn't read the fourth solution description -- the language used wasn't clear at all to me, but it was enough to point me in the right direction, or maybe I'm just that clever?

That said, I don't like interview questions like that -- there's very much a component of you either get it or you don't. The interviewer says they talk people through it, and if they're good at that, great. But if not, a question like that is (in my book) unfair.