LeetCode – Refresh – Binary Tree Zigzag 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> > zigzagLevelOrder(TreeNode *root) {
13         vector<vector<int> > result;
14         vector<int> level;
15         if (!root) return result;
16         int current = 1, future = 0;
17         bool flag = false;
18         queue<TreeNode *> q;
19         q.push(root);
20         auto func = [](int &a, int &b) {int t = a; a = b; b = t;};
21         while (!q.empty()) {
22             TreeNode *tmp = q.front();
23             q.pop(), current--;
24             if (tmp->left) {
25                 q.push(tmp->left);
26                 future++;
27             }
28             if (tmp->right) {
29                 q.push(tmp->right);
30                 future++;
31             }
32             level.push_back(tmp->val);
33             if (!current) {
34                 if (flag) {
35                     for (int i = 0; i < level.size()/2; i++) {
36                         func(level[i], level[level.size()-i-1]);
37                     }
38                 }
39                 flag ^= 1;
40                 result.push_back(level);
41                 level.clear();
42                 current = future;
43                 future = 0;
44             }
45         }
46         return result;
47     }
48 };