感觉是个后序遍历

class Solution {
public:
    void Mirror(TreeNode *pRoot){
        if(pRoot==NULL)return ;
        Mirror(pRoot->left);
        Mirror(pRoot->right);
        //下边代码原来是visit();
        TreeNode *temp=pRoot->left;
        pRoot->left=pRoot->right;
        pRoot->right=temp;
    }
};