268.md

268. Missing Number

Solution 1 (time O(n), space O(1))

class Solution(object):
    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        n = len(nums)
        expected_sum = n * (n + 1) / 2
        return expected_sum - sum(nums)