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


    }
};