Average of Levels in Binary Tree

Description

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(javascript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
const averageOfLevels = (root) => {
  
  const aux = (node, level, sums) => {
    if (!node) {
      return sums
    }
    if (node.left) {
      aux(node.left, level + 1, sums)
    }
    sums[level] = sums[level] ? {
      sum: sums[level].sum + node.val,
      counter: sums[level].counter + 1,
    } : {
      sum: node.val,
      counter: 1,
    }
    if (node.right) {
      aux(node.right, level + 1, sums)
    }
    return sums
  }
  const sums = aux(root, 0, [])
  return sums.map(({ sum, counter }) => sum / counter)
}