神、上帝以及老天爷 HDU - 2048（错排）

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 #define ll long long
 4 const int mod = 20090126;
 5 const int maxn = 21;
 6 ll c[maxn], f[maxn];
 7 void init(){
 8     c[1] = 0;
 9     c[2] = 1;
10     for(int i = 3; i < maxn; i++) {
11         c[i] = (i-1) * (c[i-1] + c[i-2]);
12     }
13     f[1] = 1;
14     for(int i = 2; i < maxn; i++) f[i] = f[i-1] * i;
15 }
16 int main(){
17     int n;
18     int t;
19     scanf("%d", &t);
20     init();
21     while(t--) {
22         scanf("%d", &n);
23         printf("%.2lf",c[n]*100.0/f[n]);
24         puts("%");
25     }
26 }