public:
    TreeNode* Mirror(TreeNode* pRoot) {
        if(!pRoot)return pRoot;
        if(pRoot){
            //交换左右子树
            TreeNode* temp=pRoot->left;
            pRoot->left=pRoot->right;
            pRoot->right=temp;
            //进入下一层递归
            Mirror(pRoot->left);
            Mirror(pRoot->right);
        }
                return pRoot;
    }
};