1 #include<iostream>
2 #include<cstdio>
3 #include<math.h>
4 #include<cstring>
5 #define INF 0x3f3f3f
6 struct node
7 {
8 double x,y,z,r;
9 }ht[105];
10 double h[105][105];
11 void prim(int n)
12 {
13 int vis[105];
14 int pos,i,j;
15 double min;
16 double tr[105];
17 memset(vis,0,sizeof(vis));
18 for(i=1;i<n;i++)
19 {
20 tr[i]=h[0][i];
21 vis[0]=1;
22 }
23 double ans=0;
24 for(i=0;i<n-1;i++)
25 {
26 min=INF;
27 for(j=1;j<n;j++)
28 {
29 if(!vis[j]&&tr[j]<min)
30 {
31 min=tr[j];
32 pos=j;
33 }
34 }
35 vis[pos]=1;
36 ans+=min;
37 for(j=1;j<n;j++)
38 {
39 if(tr[j]>h[pos][j])
40 tr[j]=h[pos][j];
41 }
42 }
43 printf("%.3f\n",ans);
44 }
45 double dis(double x1,double y1,double z1,double r1,double x2,double y2,double z2,double r2)
46 {
47 return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)+(z1-z2)*(z1-z2))-r1-r2;
48 }
49 int main()
50 {
51 int n,i,j;
52 while(~scanf("%d",&n))
53 {
54 if(n==0)
55 break;
56 for(i=0;i<n;i++)
57 {
58 scanf("%lf%lf%lf%lf",&ht[i].x,&ht[i].y,&ht[i].z,&ht[i].r);
59 }
60 memset(h,0,sizeof(h));
61 for(i=0;i<n;i++)
62 {
63 for(j=0;j<=i;j++)
64 {
65 h[i][j]=dis(ht[i].x,ht[i].y,ht[i].z,ht[i].r,ht[j].x,ht[j].y,ht[j].z,ht[j].r);
66 if(h[i][j]<0)
67 {
68 h[i][j]=0;
69
70 }
71 h[j][i]=h[i][j];
72 }
73 }
74 prim(n);
75 }
76 return 0;
77 }
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