POJ2728 Desert King

 1 /*by SilverN*/
 2 #include<algorithm>
 3 #include<iostream>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<cmath>
 7 using namespace std;
 8 const double eps=1e-4;
 9 const int mxn=1005;
10 int n,m;
11 struct node{
12     double x,y,z;
13 }p[mxn];
14 double dist(node a,node b){
15     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
16 }
17 struct edge{
18     double dis;
19     double c;
20 }mp[mxn][mxn];
21 double dis[mxn];
22 bool vis[mxn];
23 double prim(double r){
24     int i,j;
25     memset(vis,0,sizeof vis);
26     for(i=1;i<=n;i++){dis[i]=1e9;}
27     dis[1]=0;
28     double res=0;
29     while(1){
30         int pos=0;double mini=1e9;
31         for(i=1;i<=n;i++)
32             if(!vis[i] && dis[i]<mini){
33                 mini=dis[i];
34                 pos=i;
35             }
36         if(pos==0)break;
37         res+=dis[pos];
38         dis[pos]=0;vis[pos]=1;
39         for(i=1;i<=n;i++){
40             if(!vis[i])
41             dis[i]=min(dis[i],mp[pos][i].c-r*mp[pos][i].dis);
42         }
43     }
44     return res;
45 }
46 int main(){
47     while(scanf("%d",&n) && n){
48         int i,j;
49         for(i=1;i<=n;i++)
50             scanf("%lf%lf%lf",&p[i].x,&p[i].y,&p[i].z);
51         for(i=1;i<n;i++)
52          for(j=i+1;j<=n;j++){
53              mp[i][j].dis=dist(p[i],p[j]);
54              mp[i][j].c=fabs(p[i].z-p[j].z);
55              mp[j][i]=mp[i][j];
56          }
57     //    double rd;//r=sum(c)/sum(dis)
58         double l=0;double r=200;
59         while(fabs(l-r)>eps){
60             double mid=(l+r)/2;
61 //            printf("testmessage: %.4f %.4f",l,r);
62             double tmp=prim(mid);
63             if(tmp>=0)l=mid;
64             else r=mid;
65         }
66         printf("%.3f\n",l);
67     }
68     return 0;
69 }