java 反转二叉树算法

题目：Invert a binary tree.

    4   /   \  2     7 / \   / \1   3 6   9

to

     4   /   \  7     2 / \   / \9   6 3   1

下面是我给出的算法：

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