leetcode

268. Missing Number

题目描述：

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

Example 1:

Input:[3,0,1]

Output:2

Example 2:

Input:[9,6,4,2,3,5,7,0,1]

Output:8

Note:

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

分析：题目要求在线性时间复杂度，常量级额外空间完成，这就意味着无法通过排序解题，应用暴力求解，分别判断每个数字是否确实，时间超时，笔者想了一个很低端的办法，就是把给定的数组进行加和，然后利用（首项+末项）*项数/2计算给定的n的总和，将总和减去给定的每一项，最后剩下的数字即为所求

class Solution:

    def missingNumber(self, nums):

        """

        :type nums: List[int]

        :rtype: int

        """

#计算给定n值得总和

        sums = (1+len(nums))*len(nums)//2    

        for i in nums:

            sums -= i

        return sums