题目19：二叉树的镜像（leetcode链接：https://leetcode-cn.com/problems/er-cha-shu-de-jing-xiang-lcof/）

题目分析

代码描述

class Solution {
public:
    TreeNode* mirrorTree(TreeNode* root) {
        if(root == NULL || (root->left == NULL && root->right == NULL))
            return root;
        //交换左右子树的跟节点
        TreeNode* tmp = root->left;
        root->left = mirrorTree(root->right);
        root->right = mirrorTree(tmp);

        return root;
    }
};