Poj Solution 2560

http://poj.org/problem?id=2560

/* @author: */
import java.util.Scanner;
import java.util.Arrays;
public class Main{
  static double INF=99999999.0;

 public static void main(String args[])
{
 Scanner sc=new Scanner(System.in);
  
  double p[][]=new double[101][101];
  double ax[]=new double[101];
  double ay[]=new double[101];
  double dis[]=new double[101];
  boolean used[]=new boolean[101];
    int n,i,j;
      n=sc.nextInt();
    for(i=0;i< n;i++){
          ax[i]=sc.nextDouble();
          ay[i]=sc.nextDouble();
        }
    for(i=0;i< n;i++)
        for(j=0;j< n;j++) p[i][j]=INF;
    for(i=0;i< n;i++)
     for(j=i+1;j< n;j++)
     {
      double v=(ax[i]-ax[j])*(ax[i]-ax[j])+(ay[i]-ay[j])*(ay[i]-ay[j]);
      v=Math.sqrt(v);
      if(v< p[i][j])p[i][j]=p[j][i]=v;
     }
    for(i=0;i< n;i++)
        dis[i]=p[0][i];
       Arrays.fill(used,false);
    dis[0]=0;
    used[0]=true;
    double ans=0;
    for(i=0;i< n-1;i++)
    {
      double min=INF;
      int tag=-1;
      for(j=1;j< n;j++)
      {
        if(!used[j]&&dis[j]< min)
        {
        min=dis[j];
        tag=j;
         }
        }
        used[tag]=true;
        ans+=min;
        for(j=1;j< n;j++)
        {
        if(!used[j]&&dis[j]>p[tag][j])
            dis[j]=p[tag][j];
        }
     }
    System.out.printf("%3.2fn",ans);
    }
}