Inorder、Preorder、Postorder

1. Create Binary Tree (stack)
(1)Inorder
(2)Preorder
(3)Postorder
2. Parent Binary Tree (linked list 使用 parent field)
(1)Inorder
(2)Preorder
(3)Postorder
3. Thread Binary Tree (linked list 使用 引線)
(1)Inorder
(2)Preorder
4. Universal Binary Tree (stack)
(1)Inorder
(2)Preorder