Binary Tree Level Order Traversal

 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 
11 class Solution {
12 public:
13     vector<vector<int>> levelOrder(TreeNode* root) {
14         vector<vector<int>> res;
15         if(root==NULL)
16             return res;
17         TreeNode * temp;
18         queue<TreeNode *> q;
19         q.push(root);
20         while(!q.empty())  //层间循环
21         {
22             queue<TreeNode *> q2;
23             vector<int> level;
24             while(!q.empty())  //层内的节点循环
25             {
26                 temp=q.front();
27                 q.pop();
28                 level.push_back(temp->val);
29                 if(temp->left!=NULL)
30                     q2.push(temp->left);
31                 if(temp->right!=NULL)
32                     q2.push(temp->right);
33             }
34             q=q2;
35             res.push_back(level);
36         }
37         return res;
38     }
39 };