poj 2728 Desert King（最优比例生成树）

分类： Algorithm-动态规划2013-07-25
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#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;

}

}