LeetCode--Binary Tree Level Order Traversal

用两个队列实现，交叉使用，达到判断层的目的
 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         vector<vector<int> > res;
14         if(root == NULL)
15         {
16             return res;
17         }
18         queue<TreeNode *> q1;
19         queue<TreeNode *> q2;
20         q1.push(root);
21         while(!q1.empty() || !q2.empty())
22         {
23             vector<int> tmpres;
24             if(!q1.empty())
25             {
26                 while(!q1.empty())
27                 {
28                     TreeNode *tmp = q1.front();
29                     q1.pop();
30                     tmpres.push_back(tmp->val);
31                     if(tmp->left!=NULL)
32                     {
33                         q2.push(tmp->left);
34                     }
35                     if(tmp->right!=NULL)
36                     {
37                         q2.push(tmp->right);
38                     }
39                 }
40             }
41             else
42             {
43                 while(!q2.empty())
44                 {
45                     TreeNode *tmp = q2.front();
46                     q2.pop();
47                     tmpres.push_back(tmp->val);
48                     if(tmp->left!=NULL)
49                     {
50                         q1.push(tmp->left);
51                     }
52                     if(tmp->right!=NULL)
53                     {
54                         q1.push(tmp->right);
55                     }
56                 }
57             }
58             res.push_back(tmpres);
59         }
60         return res;
61     }
62 };