leetcode 103. Binary Tree Zigzag Level Order Traversal

 1 vector<vector<int> > zigzagLevelOrder(TreeNode *root) 
 2     {
 3         vector<vector<int> > result;
 4         vector<int> line;
 5         queue<TreeNode *> qtree;
 6         TreeNode *visit = root;
 7         int current_level_size = 1, next_level_size = 0;
 8         int level = 0;
 9         
10         if (visit != NULL)
11             qtree.push(visit);
12         while (!qtree.empty())
13         {
14             visit = qtree.front();
15             qtree.pop();
16             current_level_size--;
17             line.push_back(visit->val);
18             
19             if (visit->left != NULL)
20             {
21                 qtree.push(visit->left);
22                 next_level_size++;
23             }
24             if (visit->right != NULL)
25             {
26                 qtree.push(visit->right);
27                 next_level_size++;
28             }
29             if (current_level_size == 0) // all this level nodes are visited.
30             {
31                 if (level & 0x01)
32                     reverse(line.begin(), line.end());
33                 level++;
34                 result.push_back(line);
35                 line.clear();
36                 current_level_size = next_level_size;
37                 next_level_size = 0;
38             }
39         }
40         
41         return result;
42     }