Leetcode 103 Binary Tree Zigzag Level Order Traversal

triplebee

发布于 2018-01-12 14:55:31

4650

发布于 2018-01-12 14:55:31

文章被收录于专栏：计算机视觉与深度学习基础计算机视觉与深度学习基础计算机视觉与深度学习基础

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],

return its zigzag level order traversal as:

[
  [3],
  [20,9],
  [15,7]
]

二叉树蛇形层次遍历。

在第102的基础上加上一个判断奇数偶数层的标记，偶数层reverse一下。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        vector<vector<int>> res;  
        vector<int> temp;  
        queue<TreeNode*> q,q2;  
        q.push(root);  
        int flag=1;
        while(!q.empty() || !q2.empty())  
        {  
            if(q.empty())  
            {  
                swap(q,q2);
                flag++;
                if(flag%2) reverse(temp.begin(),temp.end());
                res.push_back(temp);  
                temp.clear();  
            }  
            TreeNode* first=q.front();  
            q.pop();  
            if(!first)continue;  
            temp.push_back(first->val);  
            q2.push(first->left);  
            q2.push(first->right);  
        }  
        return res;
    }
};

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原始发表：2016-10-09 ，如有侵权请联系 cloudcommunity@tencent.com 删除

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