find_all_numbers_disappeared_in_an_array.py

from typing import List

class Solution:
    """
    Task:
    Given an array nums of n integers where nums[i] is in the range [1, n],
    return an array of all the integers in the range [1, n] that do not appear in nums.
    """
    def findDisappearedNumbers(self, nums: List[int]) -> List[int]:
        n = len(nums)
        for i in range(n):
            idx = abs(nums[i]) - 1
            if nums[idx] > 0:
                nums[idx] *= -1
        res = []
        for i in range(n):
            if nums[i] > 0:
                res.append(i + 1)
        return res