【Leetcode】103. Binary Tree Zigzag Level Order Traversal（Z型按层遍历二叉树）

迈不过友情╰ 2022-02-19 10:55 192阅读 0赞

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]
    ]

题目大意：

对给出的二叉树进行Z型输出。

解题思路：

在[102题][102]的基础上对每一层的插入，输出进行调整。

/**
     * 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> > ans;
            
            if(root==NULL){
                return ans;
            }
            bool state = true;
            deque<TreeNode*> c;
            
            c.push_front(root);
            
            while(c.size()){
                ans.resize(ans.size() + 1);
                if(state){
                    for(int i = 0, og_size = c.size();i != og_size; i++){
                        auto tmp = c.front();
                        c.pop_front();
                        ans.back().push_back(tmp->val);
                        if(tmp->left) c.push_back(tmp->left);
                        if(tmp->right) c.push_back(tmp->right);
                    }
                    state = false;
                }else{
                    for(int i = 0, og_size = c.size();i != og_size; i++){
                        auto tmp = c.back();
                        c.pop_back();
                        ans.back().push_back(tmp->val);
                        if(tmp->right) c.push_front(tmp->right);
                        if(tmp->left) c.push_front(tmp->left);
                    }
                    state = true;
                }
                
            }
            
            return ans;
        }
    };

[102]: https://blog.csdn.net/qq_29600137/article/details/89318311