优选算法_锯齿形层序遍历二叉树_队列_C++

一.题目解析

就相当于蛇形遍历二叉树

算法解析:

二.代码编写:

/**
 * 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>>ret;
        if(root==nullptr)return ret;
        queue<TreeNode*>q;
        q.push(root);
        int level=1;
        while(!q.empty())
        {
            int sz=q.size();
            vector<int>tmp;
            
            for(int i=0;i<sz;i++)
            {
                TreeNode*t=q.front();
                q.pop();
                tmp.push_back(t->val);

                if(t->left)q.push(t->left);//左右孩子要入队
                if(t->right)q.push(t->right);
            }
            if(level%2==0)reverse(tmp.begin(),tmp.end());
            level++;
            ret.push_back(tmp);
        }
        return ret;
    }
};