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   7Output: [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].

 

 

还是应用广度优先遍历（BFS），然后计算每一层的和就行

 

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */import java.util.*;class Solution {    public List
     
       averageOfLevels(TreeNode root) {        Queue
      
        q=new LinkedList<>();        if(root!=null)             q.add(root);        List
       
         list=new ArrayList<>();                while(!q.isEmpty()){            int size=q.size();            double sum=0;                        for(int i=0;i