百度之星2012初赛第二场C, 网页聚类, 二分

#ifdef _MSC_VER
#define DEBUG
#define _CRT_SECURE_NO_DEPRECATE
#endif

#include <fstream>
#include <stdio.h>
#include <iostream>
#include <string.h>
#include <string>
#include <limits.h>
#include <algorithm>
#include <math.h>
#include <numeric>
#include <functional>
#include <ctype.h>
using namespace std;

const int kMAX=10010;
const double kEPS=10E-10;

struct NODE
{
double x,y,z;
}node[kMAX];

double  Distance(const NODE &lhs,const NODE &rhs)
{
return (lhs.x-rhs.x)*(lhs.x-rhs.x)+(lhs.y-rhs.y)*(lhs.y-rhs.y)+(lhs.z-rhs.z)*(lhs.z-rhs.z);
}

double map[kMAX][kMAX];
int pre[kMAX],n,m;

int Find(const int &x)
{
return x==pre[x]?x:Find(pre[x]);
}

bool Check(const double &t)
{
for(int i=0;i<n;++i)
pre[i]=i;
for(int i=0;i<n;++i)
for(int j=i+1;j<n;++j)
if(map[i][j]<t+kEPS)
{
int a=Find(i);
int b=Find(j);
pre[a]=pre[b]=pre[i]=pre[j]=min(a,b);
}
sort(pre,pre+n);
int cnt=unique(pre,pre+n)-pre;
if(cnt==m)
return true;
else
return false;
}

double BinSearch(double l,double r)
{
while(l+kEPS<r){
double mid=l+(r-l)/2;
if (Check(mid))
l=mid;
else
r=mid;
}
return l;
}

int main(void)
{
#ifdef DEBUG
freopen("../stdin.txt","r",stdin);
freopen("../stdout.txt","w",stdout);
#endif

//   scanf("%d",&ncase);

while(~scanf("%d%d",&n,&m) && n)
{
for(int i=0;i<n;++i)
scanf("%lf%lf%lf",&node[i].x,&node[i].y,&node[i].z);

double lf_max=0.0,lf_min=1e20;
for(int i=0;i<n;++i)
for(int j=i;j<n;++j)
{
map[j][i]=map[i][j]=Distance(node[i],node[j]);
lf_max=max(lf_max,map[i][j]);
lf_min=min(lf_min,map[i][j]);
}
double ans=BinSearch(lf_min,lf_max);
printf("%.6lf\n",ans);
}

return 0;
}