压扁二叉树

Flatten Binary Tree 2 Linked List

原题地址 Given a binary tree, flatten it to a linked list in-place.

For example, given the following tree:

    1
   / \
  2   5
 / \   \
3   4   6

The flattened tree should look like:

1
 \
  2
   \
    3
     \
      4
       \
        5
         \
          6
          ```

一种非常巧妙的方法：

TreeNode pre = null; public void traverse(TreeNode node){ if(node == null) return; traverse(node.right); traverse(node.left);

node.left = null;
node.right = pre;

pre = node; } ```