poj 2728 Desert King（最优比例生成树）

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <iomanip>
using namespace std;
const int maxn=1005;
const double eps=1e-6;
const double inf=0xffffffff;
struct node{
	double x,y,h;
}no[maxn];
int n;
bool visited[maxn];  

double weight[maxn][maxn],c[maxn][maxn],d[maxn][maxn];
double up,down;
double dis(node &a,node &b){
	return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
void creattree(int n,double r)
{
	for(int i=0;i<n;i++)
		for(int j=0;j<n;j++)
		{
			weight[i][j]=c[i][j]-r*d[i][j];
		}
}
void prime()
{
	up=0.0;down=0.0;
	memset(visited,0,sizeof(visited));
	int index;
	int pre[maxn];
	double dist[maxn];
	visited[1]=1;
	for(int i=0;i<n;i++)
	{
		dist[i]=weight[1][i];
		pre[i]=1;
	}
	for(int i=0;i<n;i++)
	{
		double mmimum=inf;
		for(int j=0;j<n;j++)
		{
			if(!visited[j]&&dist[j]<mmimum)
			{
				mmimum=dist[j];
				index=j;
			}
		}
		visited[index]=1;
		up+=c[pre[index]][index];
		down+=d[pre[index]][index];
		for(int i=0;i<n;i++)
		{
			if(!visited[i]&&weight[index][i]<dist[i])
			{
				dist[i]=weight[index][i];
				pre[i]=index;
			}
		}
	}

}
int main()
{
    while(scanf("%d",&n),n)
    {
    	for(int i=0;i<n;i++)
    	{
	    	scanf("%lf%lf%lf",&no[i].x,&no[i].y,&no[i].h);
	    }
	    for(int i=0;i<n;i++)
	    	for(int j=0;j<n;j++)
	    	{
	    		c[i][j]=fabs(no[i].h-no[j].h);
	    		d[i][j]=dis(no[i],no[j]);
	    	}
	    double r=30.0,ans=30.0;
		while(1)
		{
			creattree(n,r);
			prime();
			r=up/down;
			if(fabs(r-ans)<=eps)break;
			else ans=r;
		}
		printf("%.3lf\n",ans);
		//cout<<fixed<<setprecision(3)<<ans<<endl;

    }
}