226. Invert Binary Tree

Invert a binary tree.

     4
   /   
  2     7
 /    / 
1   3 6   9

     4
   /   
  7     2
 /    / 
9   6 3   1


反转一颗二叉树

c++（3ms）：

 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 public:
12     TreeNode* invertTree(TreeNode* root) {
13         if (root){
14             invertTree(root->left) ;
15             invertTree(root->right) ;
16             swap(root->left , root->right) ;
17         }
18         return root ;
19     }
20 };

C++(3ms):

 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 public:
12     TreeNode* invertTree(TreeNode* root) {
13         stack<TreeNode*> st ;
14         st.push(root) ;
15         while(!st.empty()){
16             TreeNode* t = st.top() ;
17             st.pop() ;
18             if (t){
19                 st.push(t->left) ;
20                 st.push(t->right) ;
21                 swap(t->left,t->right) ;
22             }
23         }
24         return root ;
25     }
26 };