poj Building a Space Station

http://poj.org/problem?id=2031

 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<algorithm>
 using namespace std;

 const double eps=1e-;
 const int inf=<<;
 int cmp(double x)
 {
     if(fabs(x)<eps) return ;
     if(x>) return ;
     return -;
 }

 const double pi=acos(-1.0);
 inline double sqr(double x)
 {
     return x*x;
 }

 inline double Sqrt(double a)
 {
     return a<=?:sqrt(a);
 }

 struct point
 {
    double x,y,z,r;
    point(){}
    point(double a,double b,double c,double d):x(a),y(b),z(c),r(d){}
 };

 double dis(const point &a,const point &b)
 {
     return Sqrt(sqr(a.x-b.x)+sqr(a.y-b.y)+sqr(a.z-b.z));
 }

 double dist[];
 double diss[][],ans;
 bool vis[];
 bool prime(int n)
 {
     memset(vis,,sizeof(vis));
     for(int i=; i<=n; i++)
         dist[i]=inf;
     ans=;dist[]=;
     for(int i=; i<=n; i++){
         double temp=inf;
         int k=;
         for(int j=; j<=n; j++)
         {
             if(!vis[j]&&dist[j]<temp)
             {
                 temp=dist[j];
                 k=j;
             }
         }
         if(temp==inf) return false;
         vis[k]=true;
         ans+=temp;
         for(int j=; j<=n; j++)
         {
             if(!vis[j]&&dist[j]>diss[k][j])
             {
                 dist[j]=diss[k][j];
             }
         }
     }
     return true;
 }
 int main()
 {
     int n;
     while(scanf("%d",&n)&&n)
     {
         point a[];
         memset(diss,,sizeof(diss));
         for(int i=; i<=n; i++)
         {
             scanf("%lf%lf%lf%lf",&a[i].x,&a[i].y,&a[i].z,&a[i].r);
         }
         memset(diss,,sizeof(diss));
         for(int i=; i<=n; i++)
         {
             for(int j=; j<=n; j++)
             {
                 if(dis(a[i],a[j])-a[i].r-a[j].r<=)
                 diss[i][j]=;
                 else if(dis(a[i],a[j])-a[i].r-a[j].r>eps)
                 diss[i][j]=dis(a[i],a[j])-a[i].r-a[j].r;
             }
         }
         prime(n);
         printf("%.3lf\n",ans);
     }
     return ;
 }