Find All Numbers Disappeared in an Array using Python

The challenge

Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements of [1, n] inclusive that do not appear in this array.

Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.

Example:

Input:
[4,3,2,7,8,2,3,1]
Output:
[5,6]

The solution

class Solution:
    # our method
    def findDisappearedNumbers(self, nums: List[int]) -> List[int]:
        # get the length / amount of items
        l=len(nums)
        # create a `set` to remove duplicates
        nums=set(nums)
        # create a new array to return
        d=[]

        # loop through the amount of items in the input array
        for i in range(1,l+1):
            # if the item is not in the input list
            if i not in nums:
                # add it to the return list
                d.append(i)

        # return the new array
        return d
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