Well, maybe you can use this to trick the interviewer into giving you a new problem if you don't know the first one they give you.

The article only mentioned he asked for a different problem, not that he was quickly explaining the solution and then asked for a different one. So this were exactly my thoughts, it's a bit like getting asked to find the roots of a polynom and replying "oh I already know how to do it, can you ask me something different?"

that seems very risky. it doesn't take much effort for the interviewer to spot a trickster, forfieting the interview. There is also no telling the second problem would be easier. I'd rather take my chances and hope i solve it or try to limp through with a hint.