Average of Levels in Binary Tree

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].

Note:

1. The range of node's value is in the range of 32-bit signed integer.

Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    
    public List<Double> averageOfLevels(TreeNode root) {
       List<Double> result = new ArrayList<>();
        List<Integer> list = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while(!queue.isEmpty())
        {
            int size=queue.size();
            for(int i=0;i<size;i++)
            {
                TreeNode current=queue.poll();
                list.add(current.val);
                if(current.left!=null) queue.add(current.left);
                if(current.right!=null) queue.add(current.right);
            }
            double sum=0.0,avg=0.0;
            for(int i:list)
            {
                sum+=i;
            }
            avg=sum/list.size();
            result.add(avg);
            list.clear();
        }
        return result;
    }
}