Bzoj2337 [HNOI2011]XOR和路径

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<queue>
 6 #include<cmath>
 7 using namespace std;
 8 const int mxn=20010;
 9 int read(){
10     int x=0,f=1;char ch=getchar();
11     while(ch<‘0‘ || ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
12     while(ch>=‘0‘ && ch<=‘9‘){x=x*10-‘0‘+ch;ch=getchar();}
13     return x*f;
14 }
15 struct edge{
16     int v,nxt,w;
17 }e[mxn<<1];
18 int hd[mxn],mct=0;
19 void add_edge(int u,int v,int w){
20     e[++mct].nxt=hd[u];e[mct].v=v;e[mct].w=w;hd[u]=mct;return;
21 }
22 int deg[mxn];
23 int n,m;
24 double f[300][300];
25 void Gauss(){
26     int i,j,k;
27     for(i=1;i<=n;i++){
28         int p=i;
29         for(j=i+1;j<=n;j++)
30             if(fabs(f[j][i])>fabs(f[p][i]))p=j;
31         if(p!=i)for(k=i;k<=n+1;k++)swap(f[i][k],f[p][k]);
32         for(j=i+1;j<=n;j++){
33             double c=f[j][i]/f[i][i];
34             for(k=i;k<=n+1;k++){
35                 f[j][k]-=f[i][k]*c;
36             }
37         }
38     }
39     for(i=n;i;i--){
40         double res=0;
41         for(j=i+1;j<=n;j++){
42             res+=f[j][n+1]*f[i][j];
43         }
44         f[i][n+1]=(f[i][n+1]-res)/f[i][i];
45     }
46     return;
47 }
48 int main(){
49     int i,j,u,v,w;
50     n=read();m=read();
51     for(i=1;i<=m;i++){
52         u=read();v=read();w=read();
53         add_edge(u,v,w);deg[u]++;
54         if(u!=v){add_edge(v,u,w);deg[v]++;}
55     }
56     double ans=0;
57     for(i=0;i<31;i++){
58         memset(f,0,sizeof f);
59         for(j=1;j<=n;j++)f[j][j]=1;
60         for(j=1;j<n;j++){
61             for(int k=hd[j];k;k=e[k].nxt){
62                 int v=e[k].v;
63                 if((e[k].w>>i)&1){
64                     f[j][v]+=1/(double)deg[j];
65                     f[j][n+1]+=1/(double)deg[j];
66                 }
67                 else f[j][v]-=1/(double)deg[j];
68             }
69         }
70         Gauss();
71         ans+=f[1][n+1]*(1<<i);
72     }
73     printf("%.3f\n",ans);
74     return 0;
75 }