POJ 2728

来源：互联网发布：java讲师技术含量编辑：程序博客网时间：2024/05/18 08:40

【题目分析】
最优比率生成树。

【代码】

#include <cstdio>#include <cstring>#include <cmath>#include <iostream>#include <algorithm>using namespace std;const double eps=1e-4;double x[1001],y[1001],z[1001],dis[1001];double v[1001][1001],c[1001][1001];int n,tmp,in[1001];inline bool test(double mid){    double ans=0,minn;    memset(in,0,sizeof in);     dis[1]=0;in[1]=1;    for (int i=2;i<=n;++i) dis[i]=c[1][i]-v[1][i]*mid;    for (int i=1;i<n;++i)    {        minn=0x7f7f7f7f;        for (int j=1;j<=n;++j)        if (!in[j]&&dis[j]<minn)        {            minn=dis[j];            tmp=j;        }        in[tmp]=1;        ans+=dis[tmp];        for (int j=1;j<=n;++j)            dis[j]=min(dis[j],c[tmp][j]-v[tmp][j]*mid);    }    return ans<=eps;}int main(){    while (scanf("%d",&n)!=EOF&&n)    {        for (int i=1;i<=n;++i) scanf("%lf%lf%lf",&x[i],&y[i],&z[i]);        for (int i=1;i<=n;++i)            for (int j=1;j<=n;++j)            {                v[i][j]=sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));                c[i][j]=sqrt((z[i]-z[j])*(z[i]-z[j]));            }        double l=0,r=100;        while (l+eps<=r)        {            double mid=(l+r)/2;            if (test(mid)) r=mid;            else l=mid;        }        printf("%.3f\n",l);    }}

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