LeetCode: 268. Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

For example,
Given nums = [0, 1, 3] return 2.

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

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ac:

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