Binary Tree Level Order Traversal

 1 /**
 2  * Definition for binary tree
 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         // Start typing your C/C++ solution below
14         // DO NOT write int main() function
15           vector<vector<int> > r;
16          queue<TreeNode *> q,p,useless;
17          
18          
19          
20          TreeNode * t;   
21          if(root==NULL)
22              return r;
23              
24          q.push(root);
25          
26          while(!q.empty())
27          {
28               vector<int> v;
29               while(!q.empty())
30               {
31                  
32                  t=q.front();
33                  v.push_back(t->val);
34                  q.pop();
35                  if(t->left)
36                      p.push(t->left);
37                  if(t->right)
38                      p.push(t->right);
39              }
40              q=p;
41              p=useless;
42              r.push_back(v);
43          }
44          return r;
45     }
46 };