习题2.3 数列求和-加强版

习题2.3 数列求和-加强版

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int a,n;vector<int> add(int a, int n){vector<int> B;ll sum = 0;for (int i = 0; i < n; i ++){sum += (n - i) * a;B.push_back(sum % 10);sum /= 10;}if (sum) B.push_back(sum);return B;
}int main(){vector<int> A;cin >> a >> n;if (n == 0){cout << "0";return 0;}A = add(a, n);for (int i = A.size() - 1; i >= 0; i --) cout <<A[i];return 0;
}