2176. Count Equal and Divisible Pairs in an Array

Problem

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.   Example 1:

Input: nums = [3,1,2,2,2,1,3], k = 2
Output: 4
Explanation:
There are 4 pairs that meet all the requirements:
- nums[0] == nums[6], and 0 * 6 == 0, which is divisible by 2.
- nums[2] == nums[3], and 2 * 3 == 6, which is divisible by 2.
- nums[2] == nums[4], and 2 * 4 == 8, which is divisible by 2.
- nums[3] == nums[4], and 3 * 4 == 12, which is divisible by 2.

Example 2:

Input: nums = [1,2,3,4], k = 1
Output: 0
Explanation: Since no value in nums is repeated, there are no pairs (i,j) that meet all the requirements.

  Constraints:

• 1 <= nums.length <= 100

• 1 <= nums[i], k <= 100

Solution (Java)

class Solution {
    public int countPairs(int[] nums, int k) {
        int ans = 0;
        for (int i = 0; i < nums.length; i++) {
            for (int j = i + 1; j < nums.length; j++) {
                if (nums[i] == nums[j] && (i * j) % k == 0) {
                    ++ans;
                }
            }
        }
        return ans;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).