Depth-first search binary tree problem Professor Hastings has constructed a 23-node binary tree in which each node is labeled with a unique letter of the alphabet.
Preorder and postorder traversals of the tree visit the nodes in the following order:
Preorder: B K X E H L Z J W R C Y T S Q A P D F M N U G
Postorder: H J W Z R L E C X S Q T A Y K D M U G N F P B
How can I Draw Professor Hastings' tree and list the nodes in the order visited by an inorder traversal?
 A: The first node of the preorder, which is the same as the last node in the postorder, is the root of the tree, labeled with $B$.
The node after the root in the preorder gives you the left child of the root, in this case $K$. The node before the root in the postorder gives you the right child of the root, which is labeled with $P$.
Now you look into the two subtrees with roots $K$ and $P$. These correspond to substrings in the preorder and postorder. The subtree with root $K$ corresponds to the substring starting at $K$ and ending just before $P$ in the preorder, and to the substring starting at the beginning and ending with $K$ in the postorder. The subtree with root $P$ corresponds to the substring starting with $P$ and running to the end in the preorder, and the substring starting after $K$ and ending with $P$ in the postorder. In this way, we can again find the children of $K$ and the children of $P$, same as we did for the whole tree. For $K$ they are $X$ and $Y$ in that order, and $P$ has children $D$ and $F$.
Just continue in this fashion, splitting the strings into smaller and smaller subtrees until you know the structure of the whole tree.
