Given an integer array nums, return the sum of divisors of the integers in that array that have exactly four divisors. If there is no such integer in the array, return 0.

sumFourDivisors.js

/**
 * @param {number[]} nums
 * @return {number}
 */
var sumFourDivisors = function(nums) {
    // Helper: return the sum of divisors of n if it has exactly 4 divisors.
    // Otherwise return 0.
    function sumIfFourDivisors(n) {
        let count = 0; // how many divisors we've found
        let sum = 0;   // sum of those divisors

        // Check all possible divisors from 1 up to sqrt(n)
        for (let d = 1; d * d <= n; d++) {
            if (n % d === 0) {
                let other = n / d;

                if (d === other) {
                    // d is the square root, counts as one divisor
                    count += 1;
                    sum += d;
                } else {
                    // d and n/d are two distinct divisors
                    count += 2;
                    sum += d + other;
                }

                // If we already have more than 4 divisors, we can stop early
                if (count > 4) {
                    return 0;
                }
            }
        }

        // Only numbers with exactly 4 divisors are valid
        return count === 4 ? sum : 0;
    }

    let total = 0;

    // For each number in the array, add the contribution
    for (let num of nums) {
        total += sumIfFourDivisors(num);
    }

    return total;
};