def find_duplicates(nums): tortoise = nums[0] hare = nums[0] while True: tortoise = nums[tortoise] hare = nums[hare] if tortoise == hare: break ptr1 = nums[0] ptr2 = tortoise while ptr1 != ptr2: ptr1 = nums[ptr1] ptr2 = nums[ptr2] return ptr1
print(find_duplicates([1, 2, 3, 3, 4, 5, 6]))