【模板】 prim

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<cmath>
 6 using namespace std;
 7 #define inf 1e18
 8 const int N=1000+7;
 9 struct node{
10     int x,y,z;
11 }num[N];
12 double h[N][N],len[N][N],dis[N],g[N][N];
13 bool vis[N];
14 int n;
15 bool prim(double mid){
16     memset(vis,0,sizeof(vis));
17     double sum=0;
18     for(int i=1;i<=n;++i){
19         for(int j=i+1;j<=n;++j){
20             g[i][j]=g[j][i]=h[i][j]-mid*len[i][j];
21         }
22     }
23     int all=1;
24     dis[1]=0;vis[1]=1;
25     for(int i=2;i<=n;++i) dis[i]=g[1][i];
26     for(;all<n;){
27         double minn=inf;
28         int index;
29         for(int i=1;i<=n;++i){
30             if(vis[i]==0 && dis[i]<minn){
31                 minn=dis[i];
32                 index=i;
33             }
34         }
35         vis[index]=1;
36         ++all;
37         sum+=dis[index];
38         for(int i=1;i<=n;++i)
39             if(vis[i]==0 && dis[i]>g[index][i])
40                 dis[i]=g[index][i];
41     }
42     return sum<0.0;
43 }
44 double solve(int x1,int y1,int x2,int y2){
45     double tem=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
46     return sqrt(tem);
47 }
48 int main(){
49     while(~scanf("%d",&n)&&n){
50         for(int i=1;i<=n;++i)
51             scanf("%d%d%d",&num[i].x,&num[i].y,&num[i].z);
52         for(int i=1;i<=n;++i){
53             len[i][i]=h[i][i]=0;
54            for(int j=i+1;j<=n;++j){
55                 h[i][j]=h[j][i]=abs(num[i].z-num[j].z);
56                 len[i][j]=len[j][i]=solve(num[i].x,num[i].y,num[j].x,num[j].y);
57             }
58         }
59         double l=0,r=100000.0;
60         while(r-l>1e-5){
61             double mid=(l+r)/2;
62             if(prim(mid))
63                 r=mid;else l=mid;
64         }
65         printf("%.3lf\n",r);
66     }
67     return 0;
68 }