Sum which is divisible by n in JavaScript

Problem

We are required to write a JavaScript function that takes in an array of numbers, arr, as the first argument, and a number, num, as the second argument. Our function should return the number of (contiguous, non-empty) subarrays that have a sum divisible by num.

For example, if the input to the function is −

const arr = [4, 5, 0, -2, -3, 1]; const num = 5;

Then the output should be −

const output = 7;

Output Explanation

There are 7 subarrays with a sum divisible by 5 −

[4, 5, 0, -2, -3, 1], [5], [5, 0], [5, 0, -2, -3], [0], [0, -2, -3], [-2, -3]

Example

The code for this will be −

 Live Demo

const arr = [4, 5, 0, -2, -3, 1]; const num = 5; const divisibleSum = (arr = [], num = 1) => {    const map = {};    let sum = 0;    for (let i = 0; i < arr.length; i++) {       sum += arr[i];       const key = ((sum % num) + num) % num;       map[key] = map[key]+1||1;    };    let s = 0;    for (let i = 0; i < num; i++) {       if (map[i] > 1) {          s += (map[i] * (map[i] - 1)) / 2;       }    }    return s + (map[0]||0); }; console.log(divisibleSum(arr, num));

Output

And the output in the console will be −

7