Leetcode 103. Binary Tree Zigzag Level Order Traversal

 1 /**
 2  * Definition for a binary tree node.
 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<int> row;
14         vector<vector<int>> v;
15         queue<TreeNode *> q;
16         if(root == NULL)
17             return v;
18         q.push(root);
19         TreeNode *temp;
20         int lev = 0;
21         while(!q.empty()) {
22             int size = q.size();
23             while(size--) {
24                 temp = q.front();
25                 q.pop();
26                 row.push_back(temp->val);
27                 if(temp->left != NULL) {
28                     q.push(temp->left);
29                 }
30                 if(temp->right != NULL) {
31                     q.push(temp->right);
32                 }
33             }
34             if(lev % 2) {
35                 int n = row.size();
36                 for(int i = 0; i < n/2; i++) {
37                     swap(row[i], row[n-i-1]);
38                 }
39             }
40             v.push_back(row);
41             lev++;
42             row.clear();
43         }
44         return v;
45     }
46 };

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