二叉树左右树交换

·leetcode 226题 翻转二叉树

·题目描述

给你一棵二叉树的根节点 root ，翻转这棵二叉树，并返回其根节点。

示例 1：

输入：root = [4,2,7,1,3,6,9]
输出：[4,7,2,9,6,3,1]

示例 2：

输入：root = [2,1,3]
输出：[2,3,1]

示例 3：

输入：root = []
输出：[]

·java代码

class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null) return null;
        TreeNode left = root.left;
        TreeNode right = root.right;
        root.left = right;
        root.right = left;
        invertTree(root.left);
        invertTree(root.right);
        return root;
    }
    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x) { val = x;}
        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }
}