给定一个二叉树，原地将它展开为一个单链表。

 

例如，给定二叉树

       1
    /    \
  2      5
 / \       \
3  4       6

 

将其展开为：

1
  \
   2
     \
      3
       \
        4
         \
          5
            \
             6

 

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public void flatten(TreeNode root) {
        if(root == null) {
           return;
        }
        flatten(root.left);
        flatten(root.right);
        TreeNode temp = root.right;
        root.right = root.left;
        root.left = null;
        while(root.right != null) {
            root = root.right;
        }
        root.right = temp;

    }
}

　　

 

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list
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