11_Find_All_Duplicates_in_an_Array

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