poj 2031 Building a Space Station MST

   这种n^2的，还是prim好用

/*
author:jxy
lang:C/C++
university:China,Xidian University
**If you need to reprint,please indicate the source**
*/
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#define INF 1E9
using namespace std;
struct node
{
    double x,y,z,r;
};
double d(node a,node b)
{
    double t=sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z))-a.r-b.r;
    return t>0?t:0;
}
node place[101];
bool vis[101];
double dis[101];
int main()
{
    int n;
    while(~scanf("%d",&n)&&n)
    {
        memset(vis,0,sizeof(vis));
        memset(dis,127,sizeof(dis));
        int i,j;
        for(i=0;i<n;i++)
          scanf("%lf%lf%lf%lf",&place[i].x,&place[i].y,&place[i].z,&place[i].r);
        double ans=0,Min,t;
        int now=0;
        for(i=0;i<n;i++)
        {
            Min=INF;
            for(j=0;j<n;j++)
            {
                if(dis[j]>=Min||vis[j])continue;
                Min=dis[j];now=j;
            }
            vis[now]=1;
            if(now)ans+=Min;
            for(j=0;j<n;j++)
            {
                if(vis[j])continue;
                dis[j]=min(dis[j],d(place[now],place[j]));
            }

        }
        printf("%.3f\n",ans);
    }
}