637. Average of Levels in Binary Tree

637. 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.

My Solutions:

class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        
        List<Double> list = new LinkedList<>();
        if (root == null) return list;
        Queue<TreeNode> q = new LinkedList<>();
        
        q.offer(root);
        
        while (!q.isEmpty()) {
            
            double sum = 0;
            int size = q.size();
            
            for (int i = 0; i < size; i++) {
                TreeNode n = q.poll();
                sum += n.val;
                if (n.left != null) q.offer(n.left);
                if (n.right != null) q.offer(n.right);
            }
            list.add(sum / size);
        }
        return list;
    }
}