Well, I'm not quite sure how he wrote this riddle this century, but ok.
I think you're not supposed to write anything down or anything like that when you do this, its supposed to be all in the mind. The reason I believe this is that I just got back from my psych class and the instructor showed us some questions that are on IQ tests and one was similar (but much simpler) to this one. He said that for the IQ tests you're not allowed to write anything down, and most of the people couldn't solve it.
It doesn't sound like something Einstein would have spent time doing to me. He didn't seem to like coming up with riddles for other people to solve, but just my opinion.