2176. Count Equal and Divisible Pairs in an Array

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.

class Solution {
public:
    int countPairs(vector<int>& nums, int k) {
        int res = 0;
        for(int i = 0; i < nums.size(); i++) {
            for(int j = i + 1; j < nums.size(); j++) {
                if(nums[i] == nums[j] and i * j % k == 0)
                    res++;
            }
        }
        return res;
    }
};