268. 缺失数字

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int sum = nums.size() * (nums.size() + 1) / 2;
       
        int sum2 = 0;
        for (int i = 0; i < nums.size(); i++)
        {
            sum2 += (nums[i]);
        }
       
        return sum - sum2;
    }
};