Leetcode 637 questions binary tree layer average

Topic: Given a non-empty binary tree, return an array consisting of the average value of each level of nodes.

Code

class Solution {
    
    
    public List<Double> averageOfLevels(TreeNode root)
    {
    
    
        help(root,0);
        List<Double> li =new ArrayList();
        for(int i=0;i<list.size();i++)
        {
    
       
            double nums =0;
            for(int j=0;j<list.get(i).size();j++)
            {
    
    
                nums+=list.get(i).get(j);
            }
            li.add(nums/list.get(i).size());
        }
        return li;
    }
    
    List<List<Integer>> list = new ArrayList();
    public void help(TreeNode root,int lev)//层次遍历，存储值
    {
    
       
        if(root==null)
            return;
        List<Integer> lists = new ArrayList();
        if(list.size()-1<lev)
          list.add(lists);
     
        
        list.get(lev).add(root.val); 
        help(root.left,lev+1);
        help(root.right,lev+1);
        
    }
}

First, we create a list, store all node values, store the nodes of the same level in the same element, then average the elements in each element, store it in li, and return.