226. 翻转二叉树：

题目链接 ：226. 翻转二叉树

题目：
翻转一棵二叉树。

思路：

1、递归：每层左右节点值交换

AC代码：

/**
 * 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 TreeNode invertTree(TreeNode root) {
        if(root==null)
        {
            return root;
        }
          TreeNode tmp=new TreeNode(-1);
        tmp=root.left;
        root.left=root.right;
        root.right=tmp;
        invertTree(root.left);
        invertTree(root.right);
      
        return root;
    }
   
}