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
Code language: Python (python)
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