226. 翻转二叉树

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution 
11 {
12 public:
13     TreeNode* invertTree(TreeNode* root) 
14     {
15         if(root == NULL) return NULL;
16         TreeNode* a = invertTree(root->left);
17         TreeNode* b = invertTree(root->right);
18         root->left = b;
19         root->right = a;
20         return root;
21     }
22 };