Missing Number Python Solution with Tests

lcpy gen -n 268   # by problem number
lcpy gen -s missing_number   # by problem name

Input: nums = [3,0,1]
Output: 2

Input: nums = [0,1]
Output: 2

Input: nums = [9,6,4,2,3,5,7,0,1]
Output: 8

class Solution:
    # Time: O(n)
    # Space: O(1)
    def missing_number(self, nums: list[int]) -> int:
        """
        Find the missing number in an array containing n distinct numbers
        in the range [0, n].

        Approach: Use the mathematical formula for sum of consecutive integers.
        The sum of numbers from 0 to n is n*(n+1)/2.
        The missing number = expected_sum - actual_sum.
        """
        n = len(nums)
        expected_sum = n * (n + 1) // 2
        actual_sum = sum(nums)
        return expected_sum - actual_sum