poj 2031 Building a Space Station

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

三维最小生成树

#include<iostream>
#include<cmath>
#include<string>
#include<algorithm>
#include<queue>
#include<cstring>
#include<cstdio>

using namespace std;

const int N=105;
struct node
{
    double x,y,z;
    double r;
}mem[N];
double dist[N][N];
double finddist(int i,int j)
{
    double dt=sqrt((mem[i].x-mem[j].x)*(mem[i].x-mem[j].x)
                +(mem[i].y-mem[j].y)*(mem[i].y-mem[j].y)
                   +(mem[i].z-mem[j].z)*(mem[i].z-mem[j].z));
    //cout<<mem[i].x<<" "<<mem[j].x<<endl;
    //cout<<dt<<endl;
    dt=dt-mem[i].r-mem[j].r;
    if(dt<0.0)
    dt=0.0;
    //cout<<i<<" "<<j<<" "<<dt<<endl;
    return dt;
}
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF,n)
    {
        for(int i=1;i<=n;++i)
        {
            scanf("%lf %lf %lf %lf",&mem[i].x,&mem[i].y,&mem[i].z,&mem[i].r);
            for(int j=1;j<i;++j)
            {
                dist[i][j]=dist[j][i]=finddist(i,j);
            }
        }
            double ans=0.0;
            bool had[N];
            memset(had,false,sizeof(had));
            had[1]=true;
            for(int w=1;w<n;++w)
            {
                double Min=200000.0;
                int k=0;
                for(int i=1;i<=n;++i)
                {
                    if(had[i])
                    {
                       for(int j=2;j<=n;++j)
                       {
                           if(!had[j]&&dist[i][j]<Min)
                           {
                               Min=dist[i][j];
                               k=j;
                           }
                       }
                    }
                }
                ans=ans+Min;
                had[k]=true;
            }
            printf("%.3f\n",ans);
    }
    return 0;
}