1512. Number of Good Pairs

Given an array of integers nums, return the number of good pairs.

A pair (i, j) is called good if nums[i] == nums[j] and i < j.

 

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

---

class Solution:
    def numIdenticalPairs(self, nums: List[int]) -> int:
        def fac(n):
            ans=0
            while n!=0:
                n-=1
                ans+=n
            return ans
                
        c=Counter(nums)
        ans=0
        for k,v in c.items():
            if v>=2:
                ans+=(fac(v))
        return ans