# 19.3.5 [LeetCode 103] Binary Tree Zigzag Level Order Traversal

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).

For example:
Given binary tree [3,9,20,null,null,15,7],

    3
/ \
9  20
/  \
15   7


return its zigzag level order traversal as:

[
[3],
[20,9],
[15,7]
]
 1 class Solution {
2 public:
3     vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
4         deque<TreeNode*>q,p;
5         vector<vector<int>>ans;
6         if (!root)return ans;
7         int i = 0;
8         q.push_back(root);
9         ans.push_back(vector<int>());
10         ans[0].push_back(root->val);
11         while (!q.empty()) {
12             while (!q.empty()) {
13                 TreeNode*now;
14                 if (i % 2 == 0) {
15                     now = q.front(); q.pop_front();
16                 }
17                 else {
18                     now = q.back(); q.pop_back();
19                 }
20                 if (now->left) {
21                     if (i % 2 == 0)
22                         p.push_front(now->left);
23                     else
24                         p.push_back(now->left);
25                 }
26                 if (now->right) {
27                     if (i % 2 == 0)
28                         p.push_front(now->right);
29                     else
30                         p.push_back(now->right);
31                 }
32             }
33             if(!p.empty())
34                 ans.push_back(vector<int>());
35             while (!p.empty()) {
36                 q.push_back(p.front());
37                 ans[i+1].push_back(p.front()->val);
38                 p.pop_front();
39             }
40             i++;
41         }
42         return ans;
43     }
44 };
View Code

posted @ 2019-03-05 10:35  TobicYAL  阅读(170)  评论(-1编辑  收藏  举报