Binary Tree Zigzag Level Order Traversal

 1 class Solution {
 2 public:
 3     vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
 4         vector<vector<int>> res;
 5         if(!root) return res;
 6         vector<TreeNode *> prev;
 7         vector<TreeNode *> cur;
 8         cur.push_back(root);
 9         bool even = true;
10         while(!cur.empty()){
11             vector<int> lev_res;
12             if(even){
13                 for(vector<TreeNode *>::iterator it = cur.begin(); it != cur.end(); it++)
14                     lev_res.push_back((*it)->val);
15             }else{
16                 for(vector<TreeNode *>::reverse_iterator rit = cur.rbegin(); rit != cur.rend(); rit++)
17                     lev_res.push_back((*rit)->val);
18             }
19             res.push_back(lev_res);
20             even ^= true;
21             prev = cur;
22             cur.clear();
23             for(auto i: prev){
24                 if(i->left) cur.push_back(i->left);
25                 if(i->right) cur.push_back(i->right);
26             }
27         }
28         return res;
29     }
30 };