637. 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

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * Traverse the binary tree with Breadth-First Search (BFS) algorithm
 * @param {TreeNode} root
 * @return {number[]}
 */
var averageOfLevels = function(root) {
    "use strict";
    let result = [];
    let queue = [root];
    while(queue.length) {
        let sum = 0;
        let len = queue.length;
        for (let i = 0; i < len; i++) {
            sum += queue[i].val;
            if (queue[i].left) {
                queue.push(queue[i].left);
            }
            if (queue[i].right) {
                queue.push(queue[i].right);
            }
        }
        result.push(sum / len);
        queue = queue.slice(len);
    }
    return result;
};