bzoj3925

Posted 2022-08-01 moxingtianxia

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cmath>
 4 #include<string>
 5 #include<cstring>
 6 #include<algorithm>
 7 #include<iomanip>
 8 using namespace std;
 9 namespace Moxing 
10     const int N=12,M=46;
11     int edge[N+5],cnt[1<<N+5],sz[1<<N+5],n,m;
12     long long f[1<<N+5][M+5],g[1<<N+5][M+5],c[M+5][M+5];
13     struct main 
14         main() 
15             scanf("%d%d",&n,&m);
16             for(int i=1; i<=m; i++) 
17                 int x,y;
18                 scanf("%d%d",&x,&y);
19                 x--,y--;
20                 edge[x]|=1<<y;
21                 edge[y]|=1<<x;
22             
23             c[0][0]=1;
24             for(int i=1; i<=M ; i++) 
25                 c[i][0]=c[i][i]=1;
26                 for(int j=1; j<i; j++) 
27                     c[i][j]=c[i-1][j]+c[i-1][j-1];
28                 
29             
30             int all=(1<<n)-1;
31             for(int s=1; s<=all; s++) 
32                 sz[s]=sz[s>>1]+(s&1);
33                 if(sz[s]==1) 
34                     g[s][0]=1;
35                     continue ;
36                 
37                 for(int i=0; i<n; i++) 
38                     if(s&(1<<i)) cnt[s]+=sz[edge[i]&s];
39                 
40                 cnt[s]>>=1;
41                 for(int t=s; t; t=(t-1)&s) 
42                     if(t&(s&-s)) 
43                         for(int i=0; i<=cnt[t]; i++) 
44                             for(int j=0; j<=cnt[s^t]; j++) 
45                                 f[s][i+j]+=g[t][i]*c[cnt[s^t]][j];
46                             
47                         
48                     
49 
50                 
51                 for(int i=0; i<=cnt[s]; i++) 
52                     g[s][i]=c[cnt[s]][i]-f[s][i];
53                 
54             
55             double ans=0;
56             for(int i=0; i<=m; i++) 
57                 ans+=(double)f[all][i]/c[cnt[all]][i];
58                 //cout<<f[all][i]<<‘ ‘<<c[cnt[all]][i]<<endl;
59                 //cout<<ans<<‘ ‘;
60             
61             printf("%.6lf",ans/(m+1));
62             exit(0);
63         
64      UniversalLove;
65 
66 int main() 
67     Moxing::main();
68 

View Code