poj 2728 最优比例生成树（01分数规划）模板

/*
迭代法 ：204Ms
*/
#include<stdio.h>
#include<string.h>
#include<math.h>
#define N  1100
#define eps 1e-10
#define inf  0x3fffffff
struct node {
int u,v,w;
}p
;
double ma

;
double distance(int i,int j) {
return sqrt(1.0*(p[i].u-p[j].u)*(p[i].u-p[j].u)+1.0*(p[i].v-p[j].v)*(p[i].v-p[j].v));
}
int n;
double prime(int u,double r) {
int i,j,vis
,pre
;
double dis
,len=0,cost=0,total=0;
for(i=1;i<=n;i++)  {
dis[i]=fabs(1.0*p[u].w-1.0*p[i].w)-ma[u][i]*r;
pre[i]=u;
}
memset(vis,0,sizeof(vis));
vis[1]=1;
for(i=1;i<n;i++) {
double  minn=inf;
int index=-1;
for(j=1;j<=n;j++)
if(!vis[j]&&minn>dis[j]) {
minn=dis[j];
index=j;
}
if(index!=-1) {
vis[index]=1;
len+=ma[pre[index]][index];
cost=cost+fabs(1.0*p[pre[index]].w-1.0*p[index].w);
//total+=dis[index];
for(j=1;j<=n;j++) {
double f=fabs(1.0*p[index].w-1.0*p[j].w)-ma[index][j]*r;
if(!vis[j]&&f<dis[j]) {
dis[j]=f;
pre[j]=index;
}
}
}
}
// return total;
return cost/len;
}
int main() {
int i,j;
while(scanf("%d",&n),n) {
for(i=1;i<=n;i++)
scanf("%d%d%d",&p[i].u,&p[i].v,&p[i].w);
for(i=1;i<=n-1;i++)
for(j=i+1;j<=n;j++)
ma[i][j]=ma[j][i]=distance(i,j);
/*  double l=0.0,r=100.0;
while(r-l>eps) {
double mid=(l+r)/2;
if(prime(1,mid)>=0)l=mid;
else  r=mid;
}*/
double a=0,b;
while(1) {
b=prime(1,a);
if(fabs(a-b)<eps)break;
a=b;
}
//printf("%.3f\n",r);
printf("%.3f\n",b);
}
return 0;
}

/*
二分法：1766ms
*/
#include<stdio.h>
#include<string.h>
#include<math.h>
#define N  1100
#define eps 1e-10
#define inf  0x3fffffff
struct node {
int u,v,w;
}p
;
double ma

;
double distance(int i,int j) {
return sqrt(1.0*(p[i].u-p[j].u)*(p[i].u-p[j].u)+1.0*(p[i].v-p[j].v)*(p[i].v-p[j].v));
}
int n;
double prime(int u,double r) {
int i,j,vis
,pre
;
double dis
,len=0,cost=0,total=0;
for(i=1;i<=n;i++)  {
dis[i]=fabs(1.0*p[u].w-1.0*p[i].w)-ma[u][i]*r;
pre[i]=u;
}
memset(vis,0,sizeof(vis));
vis[1]=1;
for(i=1;i<n;i++) {
double  minn=inf;
int index=-1;
for(j=1;j<=n;j++)
if(!vis[j]&&minn>dis[j]) {
minn=dis[j];
index=j;
}
if(index!=-1) {
vis[index]=1;
// len+=ma[pre[index]][index];
//cost=cost+fabs(1.0*p[pre[index]].w-1.0*p[index].w);
total+=dis[index];
for(j=1;j<=n;j++) {
double f=fabs(1.0*p[index].w-1.0*p[j].w)-ma[index][j]*r;
if(!vis[j]&&f<dis[j]) {
dis[j]=f;
pre[j]=index;
}
}
}
}
return total;
// return cost/len;
}
int main() {
int i,j;
while(scanf("%d",&n),n) {
for(i=1;i<=n;i++)
scanf("%d%d%d",&p[i].u,&p[i].v,&p[i].w);
for(i=1;i<=n-1;i++)
for(j=i+1;j<=n;j++)
ma[i][j]=ma[j][i]=distance(i,j);
double l=0.0,r=100.0;
while(r-l>eps) {
double mid=(l+r)/2;
if(prime(1,mid)>=0)l=mid;
else  r=mid;
}
/*double a=0,b;
while(1) {
b=prime(1,a);
if(fabs(a-b)<eps)break;
a=b;
}*/
printf("%.3f\n",r);
//printf("%.3f\n",b);
}
return 0;
}