[baby]

I think most people here miss the point, thinking that they need to know about symmetric binary trees in order to be able to answer such questions.

These kind of tests are aiming to find developers who can think out of the box and start solving problems they haven't heard of before. This is quite a simple problem to solve if you start thinking about it. If you get stuck because of the binary tree and because you've never done that before, then I believe you would be a mediocre dev (which is not a problem in many companies).