HDU 2048 神、上帝以及老天爷

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <bitset>
using namespace std;
typedef long long LL;
#define MOD 20090126
LL fac[25],f[25];
int T;
int main(){
  // freopen("test.in","r",stdin);
  cin >> T;
  f[1] = 0; f[2] = 1; fac[1] = 1; fac[2] = 2;
  for (int i=3;i<=20;i++){
    fac[i] = fac[i-1] * i;
    f[i] = (i-1) * (f[i-1] + f[i-2]);
  }
  for (int times = 1; times <= T; times ++){
    int n;
    cin >> n;
    printf("%.2lf%%\n", f[n] * 1.0 / fac[n] * 100);
  }
  return 0;
}