_637.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.TreeNode;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

/**
 * 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:
 The range of node's value is in the range of 32-bit signed integer.
 */
public class _637 {

    public List<Double> averageOfLevels(TreeNode root) {
        List<Double> result = new ArrayList<>();
        if (root == null) {
            return result;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            double sum = 0.0;
            for (int i = 0; i < size; i++) {
                TreeNode curr = queue.poll();
                if (curr != null) {
                    sum += curr.val;
                }
                if (curr.left != null) {
                    queue.offer(curr.left);
                }
                if (curr.right != null) {
                    queue.offer(curr.right);
                }
            }
            result.add(sum / size);
        }
        return result;
    }

}