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2176 - Count Equal and Divisible Pairs in an Array (Easy)

https://leetcode.com/problems/count-equal-and-divisible-pairs-in-an-array/

Problem Statement​

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

Approach 1: Brute Force​

Just do what it says.

Written by @wingkwong
class Solution {
public:
    int countPairs(vector<int>& nums, int k) {
        int n = nums.size(), ans = 0;
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                ans += nums[i] == nums[j] && (i * j) % k == 0;
            }
        }
        return ans;
    }
};