442. Find All Duplicates in an Array.py

class Solution:
    def findDuplicates(self, nums: List[int]) -> List[int]:
        res = []
        for i in range(len(nums)):
            if nums[ abs(nums[i]) - 1] < 0:
                res.append(abs(nums[i]))
            else:
                nums[ abs(nums[i]) - 1] *= -1
        return res