[Leetcode] 442. Find All Duplicates in an Array

https://leetcode.com/problems/find-all-duplicates-in-an-array

class Solution:
    def findDuplicates(self, nums: List[int]) -> List[int]:
        result = []

        nums_set = set()

        for n in nums:
            if n in nums_set:
                result.append(n)
            else:
                nums_set.add(n)

        return result