C++ 高效计算 S = 1 + (1+2) + (1+2+3) + ... + (1+2+3+...+n)

#include using namespace std;

int main() { int n; cin >> n;

int s = 0;
int sum = 0;

for(int i=1; i<=n; i++) {
    sum += i;
    s += sum;
}

cout << s << endl;

return 0;

}