PreOrderBuildTree  -  hints

• Loop through the two lists backwards, building the tree from the bottom-up. For example, the last item in the list must be a leaf.
• Push a partial tree you build in a Stack <BinaryNode> temporarily until you reach its parent in the list, at which time you can pop it off and set it as a child of the parent.
• Have fun. This is a really neat problem that again shows how useful stacks are. :)