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.

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.

def countPairs(self, nums: List[int], k: int) -> int:
	pos = defaultdict(list)
	count = 0

	for i, num in enumerate(nums):
		for j in pos[num]:
			if (i * j) % k == 0:
				count += 1
		pos[num].append(i)

	return count