[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?

class Solution {public:    int missingNumber(vector<int>& nums) {        const int n = nums.size();        int expected = (1 + n) * n / 2;        int actual = accumulate(nums.begin(), nums.end(), 0);        return expected - actual;    }};