自己运行跟答案一样，但不过

#include<iostream>
using namespace std;
int n, hyt, a[105], s[105];
void add()
{
    int extra;
    for (int i = 100; i >= 0; i--)
    {
        s[i] = s[i] + a[i] + extra;
        extra = s[i] / 10;
        s[i] %= 10;
    }
}
void mul(int x)
{
    int extra;
    for (int i = 100; i >= 0; i--)
    {
        a[i]= a[i] * x + extra;
        extra = a[i] / 10;
        a[i] %= 10;
    }
}
int main()
{
    cin >> n;
    a[100] = s[100] = 1;
    for (int i = 2; i <= n; i++)
        mul(i), add();
    for (int i = 0; i <= 100; i++)
        if (s[i])
        {
            hyt = i;
            break;
        }
    for (int i = hyt; i <= 100; i++)
       cout << s[i];
    return 0;
}