Coursera Algorithms week4 基础标签表 练习测验：Inorder traversal with constant extra space

题目原文：

Design an algorithm to perform an inorder traversal of a binary search tree using only a constant amount of extra space.

 public void traverse(BST<Key,Value> bst) {
     traverse(bst.root.left, bst.root);
 }
 
 private void traverse(Node current, Node parent) {
     while (current != null) {
         if (parent != null) {
             parent.left = current.right;
             current.right = parent;
         }
         if (current.left != null) {
             parent = current;
             current = current.left;
         } else {
             System.out.println(current.key);
             current = current.right;
             parent = null;
         }
     }
 }