226. Invert Binary Tree

左右翻转一棵树，两种方法

第一种是非递归方法，借助层次遍历来实现，交换每一个节点的左右子节点即可

 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==NULL)
14             return NULL;
15         queue<TreeNode*> que;
16         que.push(root);
17         while(!que.empty())
18         {
19             TreeNode* p=que.front();
20             que.pop();
21             TreeNode* temp=p->left;
22             p->left=p->right;
23             p->right=temp;
24             if(p->left!=NULL)
25                 que.push(p->left);
26             if(p->right!=NULL)
27                 que.push(p->right);
28         }
29         return root;
30     }
31 };

第二种方法是递归，递归交换所有节点的左右子节点

 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 static int wing=[]()
11 {
12     std::ios::sync_with_stdio(false);
13     cin.tie(NULL);
14     return 0;
15 }();
16 
17 class Solution 
18 {
19 public:
20     TreeNode* invertTree(TreeNode* root) 
21     {
22         change(root);
23         return root;
24     }
25     
26     void change(TreeNode * root)
27     {
28         if(root==NULL)
29             return;
30         TreeNode *temp=root->right;
31         root->right=root->left;
32         root->left=temp;
33         change(root->left);
34         change(root->right);
35     }
36     
37     
38 };