【HDU4035】Maze

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <iostream>
 5 #include <vector>
 6 #include <cmath>
 7 
 8 using namespace std;
 9 const int maxn=10000+100;
10 int T,n;
11 double E[maxn],K[maxn],A[maxn],B[maxn],C[maxn];
12 vector<int>G[maxn];
13 bool dfs(int u,int fa){
14      double temp=0;
15      if(G[u].size()==1&&fa!=-1){
16          A[u]=K[u];
17          B[u]=1-K[u]-E[u];
18          C[u]=1-K[u]-E[u];
19          return true;
20      }
21      A[u]=K[u];
22      B[u]=(1-K[u]-E[u])/G[u].size();
23      C[u]=1-K[u]-E[u];
24     for(int i=0;i<G[u].size();i++){
25         int v=G[u][i];
26         if(v!=fa){
27             if(!dfs(v,u))return false;
28             A[u]+=A[v]*(1-K[u]-E[u])/G[u].size();
29             C[u]+=(1-K[u]-E[u])/G[u].size()*C[v];
30             temp+=B[v]*(1-K[u]-E[u])/G[u].size();
31         }
32     }
33     if(fabs(1-temp)<=1e-10)return false;
34     A[u]/=(1-temp);
35     B[u]/=(1-temp);
36     C[u]/=(1-temp);
37     return true;
38 }
39 int main(){
40     scanf("%d",&T);
41     for(int t=1;t<=T;t++){
42         memset(A,0,sizeof(A));
43         memset(B,0,sizeof(B));
44         memset(C,0,sizeof(C));
45         scanf("%d",&n);
46         for(int i=1;i<=n;i++)G[i].clear();
47         int x,y;
48         for(int i=1;i<n;i++){
49             scanf("%d%d",&x,&y);
50             G[x].push_back(y);
51             G[y].push_back(x);
52         }
53         for(int i=1;i<=n;i++){
54             scanf("%lf%lf",&K[i],&E[i]);
55             K[i]/=100,E[i]/=100;
56         }
57         printf("Case %d: ",t);
58         if(!dfs(1,-1)||(1-A[1])<=1e-10){
59             printf("impossible\n");
60             continue;
61         }
62        /* for(int i=1;i<=n;i++){
63             cout<<i<<" "<<C[i]<<endl;
64         }*/
65         printf("%.6f\n",C[1]/(1-A[1]));
66     }
67 return 0;
68 }