同LeetCode226翻转二叉树

 1 class Solution {
 2 public:
 3     TreeNode* mirrorTree(TreeNode* root) {
 4         if(root == NULL) return NULL;
 5         TreeNode* node = root->left;
 6         root->left = root->right; root->right = node;
 7         mirrorTree(root->left);
 8         mirrorTree(root->right);
 9         return root;
10     }
11 };