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###### tags: `Leetcode`

# 103. Binary Tree Zigzag Level Order Traversal

###### Link : https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/description/

## 題目
求樹的Zigzag levelorder
Zigzag levelorder:
1. 必須分層
2. 第一層由左至右，第二層由右至左，以此類推
## 程式碼

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        vector<vector<int>> ans;
        queue<TreeNode *> q;
        int i = 0;
        if(root) q.push(root);
        while(!q.empty()){
            int size = q.size();
            vector<int> temp;
            for(int i = 0;i < size;++i){
                TreeNode* node = q.front(); q.pop();
                temp.push_back(node->val);
                if(node->left) q.push(node->left);
                if(node->right) q.push(node->right);
            }
            if(i++ & 1) reverse(temp.begin(), temp.end());
            ans.push_back(temp);
        }
        return ans;
    }
};