【HDU4035】Maze

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <vector>
#include <cmath>

using namespace std;
const int maxn=10000+100;
int T,n;
double E[maxn],K[maxn],A[maxn],B[maxn],C[maxn];
vector<int>G[maxn];
bool dfs(int u,int fa){
     double temp=0;
     if(G[u].size()==1&&fa!=-1){
         A[u]=K[u];
         B[u]=1-K[u]-E[u];
         C[u]=1-K[u]-E[u];
         return true;
     }
     A[u]=K[u];
     B[u]=(1-K[u]-E[u])/G[u].size();
     C[u]=1-K[u]-E[u];
    for(int i=0;i<G[u].size();i++){
        int v=G[u][i];
        if(v!=fa){
            if(!dfs(v,u))return false;
            A[u]+=A[v]*(1-K[u]-E[u])/G[u].size();
            C[u]+=(1-K[u]-E[u])/G[u].size()*C[v];
            temp+=B[v]*(1-K[u]-E[u])/G[u].size();
        }
    }
    if(fabs(1-temp)<=1e-10)return false;
    A[u]/=(1-temp);
    B[u]/=(1-temp);
    C[u]/=(1-temp);
    return true;
}
int main(){
    scanf("%d",&T);
    for(int t=1;t<=T;t++){
        memset(A,0,sizeof(A));
        memset(B,0,sizeof(B));
        memset(C,0,sizeof(C));
        scanf("%d",&n);
        for(int i=1;i<=n;i++)G[i].clear();
        int x,y;
        for(int i=1;i<n;i++){
            scanf("%d%d",&x,&y);
            G[x].push_back(y);
            G[y].push_back(x);
        }
        for(int i=1;i<=n;i++){
            scanf("%lf%lf",&K[i],&E[i]);
            K[i]/=100,E[i]/=100;
        }
        printf("Case %d: ",t);
        if(!dfs(1,-1)||(1-A[1])<=1e-10){
            printf("impossible
");
            continue;
        }
       /* for(int i=1;i<=n;i++){
            cout<<i<<" "<<C[i]<<endl;
        }*/
        printf("%.6f
",C[1]/(1-A[1]));
    }
return 0;
}