Leetcode -- Binary Tree Level Order Traversal

 /**  
  * Definition for binary tree  
  * struct TreeNode {  
  *   int val;  
  *   TreeNode *left;  
  *   TreeNode *right;  
  *   TreeNode(int x) : val(x), left(NULL), right(NULL) {}  
  * };  
  */  
 class Solution {  
 public:  
   vector<vector<int> > levelOrder(TreeNode *root) {  
     vector<vector<int> > result;  
     if(root == NULL) {  
       return result;  
     }  
     queue<TreeNode *> q;  
     q.push(root);  
     while(!q.empty()) {  
       queue<TreeNode *> temp;  
       vector<int> toInsert;  
       while(!q.empty()) {  
         TreeNode * t = q.front();  
         q.pop();  
         toInsert.emplace_back(t->val);  
         if(t->left != NULL) {  
           temp.push(t->left);  
         }  
         if(t->right != NULL) {  
           temp.push(t->right);  
         }  
       }  
       result.emplace_back(toInsert);  
       swap(q, temp);  
     }  
     return result;  
   }  
 };