层序遍历

 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     vector<vector<int>> levelOrder(TreeNode* root) {
13         vector<vector<int>> vec; 
14         if(!root) return vec;   
15         queue<TreeNode*> q;
16         q.push(root);
17         while(!q.empty())
18         {
19             vector<int> tmp;
20             int len=q.size();
21             for(int i=0;i<len;i++)
22             {
23                 TreeNode* front=q.front();
24                 tmp.push_back(front->val);
25                 q.pop();
26                 if(front->left) q.push(front->left);
27                 if(front->right) q.push(front->right);
28             }
29             vec.push_back(tmp);
30         }
31         return vec; 
32     }
33 };