代码不长，我让循环中所有要做的事全做完了，不另外开循环，这样省了很多时间

#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1e5+10;
int a[N],b[N];
int top = 1,siz_a=1;
signed main()
{
    int n;cin >>n;
    b[1] = 1;
    for(int i = 1 ; i <= n ; i++) {
        for(int j = 1 ; j <= top ; j++){
            b[j]*=i;
        }
        if(siz_a<top) siz_a = top;
        for(int j = 1 ; j <= siz_a ; j++){
            if(b[j]>9&&j<=top){
                b[j+1] +=b[j]/10;
                b[j]%=10;
                if(j+1>top) top++,siz_a++;
            }
            if(j<=top) a[j]+=b[j];
            if(a[j]>9){
                a[j+1]+=a[j]/10;
                a[j]%=10;
                if(j+1>siz_a) siz_a++;
            }
        }
    }
    for(int i = siz_a ; i >= 1 ; i--) cout << a[i];
    cout << endl;
    return 0;
}