442. Find All Duplicates in an Array (Medium) - TengnanYao/daily_leetcode GitHub Wiki

class Solution:
    def findDuplicates(self, nums: List[int]) -> List[int]:
        # their solution
        res = []
        for x in nums:
            if nums[abs(x) - 1] < 0:
                res.append(abs(x))
            else:
                nums[abs(x) - 1] *= -1
        return res
        
        # my solution
        result = set()
        i = 0
        while i < len(nums):
            if nums[i] != i + 1:
                t = nums[i] - 1
                if nums[t] == nums[i]:
                    result.add(nums[i])
                    i += 1
                else:
                    nums[i], nums[t] = nums[t], nums[i]
            else:
                i += 1
        return result