hdu1465 不容易系列之一 裸错排

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <cmath>using namespace std;unsigned long long  f[205];int main(){    f[1]=0;    f[2]=1;    for(int i=3;i<=25;i++)        f[i]=(i-1)*(f[i-1]+f[i-2]);       unsigned long long  n,m;    while(cin>>n)    {        cout<<f[n]<<endl;    }}