1512. Number of Good Pairs

https://leetcode.com/problems/number-of-good-pairs

Python

from math import factorial
from collections import defaultdict


class Solution:
    def numIdenticalPairs(self, nums: List[int]) -> int:
        mapper = defaultdict(int)

        for i, num in enumerate(nums):
            mapper[num] += 1

        ans = 0
        for count in mapper.values():
            if count >= 2:
                # C = n! / m!(n-m!)
                ans += (
                    factorial(count)/
                    (2*factorial(count-2))
                )

        return int(ans)