LeetCode 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.

Constraints:

• 1 <= nums.length <= 100

• 1 <= nums[i], k <= 100

• Easy 题目，遍历即可。

Runtime: 3 ms, faster than 99.48% of Java online submissions for Count Equal and Divisible Pairs in an Array.

Memory Usage: 42.4 MB, less than 31.63% of Java online submissions for Count Equal and Divisible Pairs in an Array.