LeetCode: Average Of Levels In Binary Tree Solution

1/**
2 * Definition for a binary tree node.
3 * function TreeNode(val, left, right) {
4 *     this.val = (val===undefined ? 0 : val)
5 *     this.left = (left===undefined ? null : left)
6 *     this.right = (right===undefined ? null : right)
7 * }
8 */
9/**
10 * @param {TreeNode} root
11 * @return {number[]}
12 */
13var averageOfLevels = function (root) {
14  const average = arr => arr.reduce((acc, el) => acc + el, 0) / arr.length
15  const valuesAtDepth = []
16
17  const recursion = function (node, depth = 0) {
18    if (!node) {
19      return
20    }
21
22    if (!valuesAtDepth[depth]) {
23      valuesAtDepth[depth] = []
24    }
25    valuesAtDepth[depth].push(node.val)
26    recursion(node.left, depth + 1)
27    recursion(node.right, depth + 1)
28  }
29
30  recursion(root)
31
32  return valuesAtDepth.map(average)
33}