I found an interesting problem on https://leetcode.com/problems/number-of-good-pairs/:
Given an array of integers nums.
A pair (i,j) is called good if nums[i] == nums[j] and i < j.
Return the number of good pairs.
 
Example 1:
Input: nums = [1,2,3,1,1,3]
Output: 4
Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed.

Example 2:
Input: nums = [1,1,1,1]
Output: 6
Explanation: Each pair in the array are good.

Example 3:
Input: nums = [1,2,3]
Output: 0

 
Constraints:

1 <= nums.length <= 100
1 <= nums[i] <= 100

I tried it in Python, but could not do it. Can you solve it?
class Solution:
    def numIdenticalPairs(self, nums: List[int]) -> int:
        tracker = {}
        
        for num in nums:
            if num not in tracker:
                tracker[num] = 0
            else:
                tracker[num] += 1
        
        sum = 0
        for num in tracker:
            sum += tracker[num] * (tracker[num]+1) // 2
        return sum