BZOJ 3925 [Zjoi2015]地震后的幻想乡 一道积分神题

Posted 2020-10-29 Stump

https://www.lydsy.com/JudgeOnline/showsource.php?id=2689580

 

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring>
 4 using namespace std;
 5 typedef double db;
 6 const int N=10,M=46;
 7 int x,y,n,m;
 8 int sz[1<<N],link[1<<N];
 9 db f[1<<N][M];
10 int main(){
11     scanf("%d%d",&n,&m);
12     for(register int i=0;i<m;++i){
13         scanf("%d%d",&x,&y);
14         --x,--y;
15         link[x]|=(1<<y),link[y]|=(1<<x);
16     }
17     for(register int i=1;i<(1<<n);++i)
18         sz[i]=sz[i>>1]+(i&1);
19     for(register int S1=1;S1<(1<<n);++S1)
20         if(S1&1){
21             for(register int S2=(S1-1)&S1;S2;S2=(S2-1)&S1)
22                 if(S2&1){
23                     int T=0;
24                     for(register int i=0;i<n;++i)
25                         if((S1>>i)&(~S2>>i)&1)
26                             T+=sz[link[i]&S2];
27                     for(register int i=0;i+T<=m;++i)
28                         f[S1][i]+=1.00/(i+1+T)-f[S2][i+T];
29                 }
30         }
31     printf("%.6lf\\n",f[(1<<n)-1][0]);
32     return 0;
33 }

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