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.

class Solution {

    public List<Double> averageOfLevels(TreeNode root) {

        List<Double> result = new ArrayList<>();

        Queue<TreeNode> q = new LinkedList<>();

 

        if (root == null)

　　　　return result;

        q.add(root);

        while (!q.isEmpty()) {

            int n = q.size();

            double sum = 0;

            for (int i = 0; i < n; i++) {

                TreeNode node = q.poll();

                sum += node.val;

                if (node.left != null) q.offer(node.left);

                if (node.right != null) q.offer(node.right);

            }

            result.add(sum / n);

        }

        return result;

    }

}