637. Average of Levels in Binary Tree

Posted 2020-10-18 西瓜刀刀刀

Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

Example 1:

Input:
    3
   /   9  20
    /     15   7
Output: [3, 14.5, 11]
Explanation:
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

（1）思想1：使用queue ，对二叉树进行层遍历。

C++：

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     vector<double> averageOfLevels(TreeNode* root) {
13         vector<double> res;
14         queue<TreeNode*> q{{root}};
15         while(!q.empty())
16         {
17             int n=q.size();
18             double sum=0;
19             for(int i=0;i<n;i++)
20             {
21                 TreeNode *t=q.front();
22                 q.pop();
23                 sum=sum+t->val;
24                 if(t->left)
25                     q.push(t->left);
26                 if(t->right)
27                     q.push(t->right);
28             }
29             res.push_back(sum/n);
30         }
31         return res;
32      
33     }
34 };