18.二叉树的镜像

URL：https://www.nowcoder.com/practice/a9d0ecbacef9410ca97463e4a5c83be7?tpId=13&tqId=11171&rp=1&ru=%2Fta%2Fcoding-interviews&qru=%2Fta%2Fcoding-interviews%2Fquestion-ranking&tab=answerKey

/**
 * struct TreeNode {
 *    int val;
 *    struct TreeNode *left;
 *    struct TreeNode *right;
 *    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param pRoot TreeNode类 
     * @return TreeNode类
     */
     TreeNode *Mirror(TreeNode *pRoot) {
        // write code here
        if (pRoot == nullptr) {
            return nullptr;
        }
        TreeNode *tmp = pRoot->left;
        pRoot->left = pRoot->right;
        pRoot->right = tmp;
        Mirror(pRoot->right);
        Mirror(pRoot->left);
        return pRoot;
    }
};