number-of-subarrays.js

/*
Given an array of integers arr and two integers k and threshold, return the number of sub-arrays of size k and average greater than or equal to threshold.

Example 1:

Input: arr = [2,2,2,2,5,5,5,8], k = 3, threshold = 4
Output: 3
Explanation: Sub-arrays [2,5,5],[5,5,5] and [5,5,8] have averages 4, 5 and 6 respectively. All other sub-arrays of size 3 have averages less than 4 (the threshold).

Example 2:

Input: arr = [11,13,17,23,29,31,7,5,2,3], k = 3, threshold = 5
Output: 6
Explanation: The first 6 sub-arrays of size 3 have averages greater than 5. Note that averages are not integers.

*/

var numOfSubarrays = function (arr, k, threshold) {
	let result = 0;
	let currSum = arr.slice(0, k - 1).reduce((acc, val) => acc + val, 0); // already build a window

	for (let l = 0; l <= arr.length - k; l++) {
		currSum += arr[l + k - 1];

		if (currSum / k >= threshold) result += 1;

		currSum -= arr[l];
	}

	return result;
};