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

SOLUTION:

class Solution:
    def numIdenticalPairs(self, nums: List[int]) -> int:
        n = len(nums)
        valIndexes = {}
        total = 0
        for i in range(n):
            valIndexes[nums[i]] = valIndexes.get(nums[i], 0) + 1
        for val in valIndexes:
            freq = valIndexes[val]
            total += freq * (freq - 1) // 2
        return total