Brute Force

'''
Time: O(log n) sorting
Space: O(1)
'''
class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        nums.sort()
        n = len(nums)

        if nums[0] != 0:
            return 0
        if nums[n - 1] != n:
            return n

        for i in range(n - 1):
            if nums[i + 1] != nums[i] + 1:
                return nums[i] + 1
        return -1