hdu 4336 概率dp

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<cmath>
 6 #include<queue>
 7 #include<map>
 8 using namespace std;
 9 #define MOD 1000000007
10 const double eps=1e-5;
11 #define cl(a) memset(a,0,sizeof(a))
12 #define ts printf("*****\n");
13 const int MAXN=22;
14 int n,m,tt;
15 double a[MAXN];
16 double dp[1<<22];
17 int main()
18 {
19     int i,j,k;
20     #ifndef ONLINE_JUDGE
21     freopen("1.in","r",stdin);
22     #endif
23     while(scanf("%d",&n)!=EOF)
24     {
25         double tt=0;
26         for(i=0;i<n;i++)    scanf("%lf",&a[i]),tt+=a[i];
27         dp[(1<<n)-1]=0;
28         tt=1-tt;
29         for(i=(1<<n)-2;i>=0;i--)
30         {
31             double sum=1,x=0;
32             for(j=0;j<n;j++)
33             {
34                 if(i&(1<<j))
35                 {
36                     x+=a[j];        //出现的卡片原来有了
37                 }
38                 else
39                 {
40                     sum+=a[j]*dp[i|(1<<j)];
41                 }
42             }
43             dp[i]=sum/(1-tt-x);
44         }
45         printf("%.5lf\n",dp[0]);
46     }
47     return 0;
48 }