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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class Solution {public:    int missingNumber(vector<int>& nums) {        double sum=(nums.size())*(nums.size()+1)/2;        for(int i=0;i<nums.size();++i)        {            sum-=nums[i];        }        return sum;    }};