Given a 0-indexed integer array nums of length n and an integer k, return the number of pairs (i, j) where 0 <= i < j < n, such that nums[i] == nums[j] and (i * j) is divisible by k.

countPairs.js

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
var countPairs = function(nums, k) {
    // Initialize a counter to keep track of pairs that satisfy the conditions
    let count = 0;

    // Loop through all possible values of i (starting from index 0)
    for (let i = 0; i < nums.length; i++) {
        // For each i, loop through all possible values of j (starting from i + 1)
        for (let j = i + 1; j < nums.length; j++) {
            // Check if the values at indices i and j are equal
            if (nums[i] === nums[j]) {
                // Check if the product of i and j is divisible by k
                if ((i * j) % k === 0) {
                    // Increment the counter if both conditions are satisfied
                    count++;
                }
            }
        }
    }
    // Return the total count of valid pairs
    return count;
};