leetcode------Flatten Binary Tree to Linked List

标题:	Flatten Binary Tree to Linked List
通过率：	28.7%
难度：	中等

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

For example,
Given

         1
        / 
       2   5
      /    
     3   4   6

The flattened tree should look like:

   1
    
     2
      
       3
        
         4
          
           5
            
             6

click to show hints.

Hints:

If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.

本题就是把一颗树变成退化树

都是只有右孩子，那么需要操作的就是找到左孩子的最有节点，将root的右树连接到左孩子的最右节点，然后root的右孩子指向左孩子，root的左孩子置空

看代码具体操作：

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public void flatten(TreeNode root) {
       while(root!=null){
           if(root.left!=null){
            TreeNode tmp=root.left;
            while(tmp.right!=null)
                tmp=tmp.right;
            tmp.right=root.right;
            root.right=root.left;
            root.left=null;
           }
            root=root.right;
       }
    }
}