Missing Number 第一个缺失的数

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:
    //方法一：排序 然后遍历一下 时间不是线性 
    //因为是连续的 可以直接计算和 然后减去各个值即可
    int missingNumber(vector<int>& nums) {
    
        int n=nums.size();
        int ans=(1+n)*n/2;
        for(int i=0;i<n;i++)
            ans-=nums[i];
        return ans;
    }
};