Permutation Leetcode

Question

I was solving this leetcode permutation problem and came across an error that am getting n empty lists inside my returned list which suppose to print different permutations of the given list

getting output => [[], [], [], [], [], []]

Expected output=> [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

def permute(nums):
    l=[]
    s=list()
    ans=[]

        return helper(nums,s,l)
def helper(nums,s,l):
    if not nums:
        print(l)
        s.append(l)
    else:
        for i in range(len(nums)):
            c=nums[i]
            l.append(c)
            nums.pop(i)
            helper(nums,s,l)
            nums.insert(i,c)
            l.pop()
    return s
print(permute([1,2,3]))

Answer 1

You should do s.append(l.copy()) because otherwise you pop all values from the same list l, that's why the result consists of empty lists.