题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3622
题意：一个平面上有很多的炸弹，每个炸弹的爆炸范围是一样的，求最大的爆炸范围使得炸弹之间不相互影响。
二分爆炸范围，然后建立2sat模型，看是否存在解。
//STATUS:C++_AC_171MS_972KB
#include <functional>
#include <algorithm>
#include <iostream>
//#include <ext/rope>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cstring>
#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bitset>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <list>
#include <set>
#include <map>
using namespace std;
//using namespace __gnu_cxx;
//define
#define pii pair<int,int>
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define PI acos(-1.0)
//typedef
typedef long long LL;
typedef unsigned long long ULL;
//const
const int N=;
const int INF=0x3f3f3f3f;
const int MOD=,STA=;
const LL LNF=1LL<<;
const double EPS=1e-;
const double OO=1e15;
const int dx[]={-,,,};
const int dy[]={,,,-};
const int day[]={,,,,,,,,,,,,};
//Daily Use ...
inline int sign(double x){return (x>EPS)-(x<-EPS);}
template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
template<class T> inline T Min(T a,T b){return a<b?a:b;}
template<class T> inline T Max(T a,T b){return a>b?a:b;}
template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
//End double d[N][N];
int nod[N][];
int first[N],next[N*N*],vis[N],S[N];
int n,mt,cnt; struct Edge{
int u,v;
}e[N*N*]; double dist(int i,int j){
return sqrt((double)((nod[i][]-nod[j][])*(nod[i][]-nod[j][])+
(nod[i][]-nod[j][])*(nod[i][]-nod[j][])));
} void adde(int a,int b)
{
e[mt].u=a,e[mt].v=b;
next[mt]=first[a];first[a]=mt++;
} int dfs(int u)
{
if(vis[u^])return ;
if(vis[u])return ;
int i;
vis[u]=;
S[cnt++]=u;
for(i=first[u];i!=-;i=next[i]){
if(!dfs(e[i].v))return ;
}
return ;
} int Twosat()
{
int i,j;
for(i=;i<n;i+=){
if(vis[i] || vis[i^])continue;
cnt=;
if(!dfs(i)){
while(cnt)vis[S[--cnt]]=;
if(!dfs(i^))return ;
}
}
return ;
} void init(double limt)
{
int i,j;
mt=;mem(vis,);
mem(first,-);
for(i=;i<n;i++){
for(j=i+;j<n;j++)if(d[i][j]<limt)adde(i,j^),adde(j,i^);
i++;
for(j=i+;j<n;j++)if(d[i][j]<limt)adde(i,j^),adde(j,i^);
}
} double binary(double l,double r)
{
double mid;
while(fabs(l-r)>EPS){
mid=(l+r)/;
// printf("%.2lf %.2lf %.2lf\n",l,r,mid);
init(mid);
if(Twosat())l=mid;
else r=mid;
}
return mid;
} int main()
{
// freopen("in.txt","r",stdin);
int i,j;
double hig;
while(~scanf("%d",&n))
{
n<<=;
for(i=;i<n;i+=){
scanf("%d%d%d%d",&nod[i][],&nod[i][],&nod[i^][],&nod[i^][]);
}
hig=;
for(i=;i<n;i++){
for(j=i+;j<n;j++){
d[i][j]=d[j][i]=dist(i,j);
hig=Max(hig,d[i][j]);
}
} printf("%.2lf\n",binary(,hig)/);
}
return ;
}