HDU 3622 Bomb Game

#include <bits/stdc++.h>
using namespace std;

#define F first
#define S second
#define mpr make_pair
#define sqr(x) ((x)*(x))
const int N = 205;
const double eps = 1e-5;
typedef pair< int,int > pr;
typedef pair< pr,pr > prr;

int n,c,cnt,cntb;
pr a[N];
vector< int > g[N];
int d[N],b[N];
int stk[N],instk[N],top;

inline int in(int x=0) { scanf("%d",&x);return x; }
void clr() {
	cntb=cnt=top=0;
	for(int i=0;i<N;i++) g[i].clear();
	memset(d,0,sizeof(d)),memset(b,0,sizeof(b)),memset(instk,0,sizeof(instk));
}
double Dist(pr x,pr y) { return sqrt((double)sqr(x.F-y.F)+sqr(x.S-y.S)); }
void Tarjan(int u,int fa) {
	d[u]=++cnt,stk[++top]=u,instk[u]=1;int dfsn=cnt;
	for(int i=0,v;i<(int)g[u].size();i++) if((v=g[u][i])!=fa) {
		if(!d[v]) Tarjan(v,u);
		if(instk[v]) d[u]=min(d[u],d[v]);
	}
	if(d[u]==dfsn) {
		for(++cntb;stk[top]!=u;top--) {
			b[stk[top]]=cntb,instk[stk[top]]=0;
		}b[stk[top]]=cntb,instk[stk[top--]]=0;
	}
//	cout<<u<<":"<<d[u]<<" "<<dfsn<<endl;
}
int check(double x) {
	clr();
	for(int i=0;i<c;i++) for(int j=i&1 ? i+1 : i+2;j<c;j++)
		if(Dist(a[i],a[j])<x*2) g[i].push_back(j^1),g[j].push_back(i^1);
//	cout<<"("<<i<<","<<j<<")"<<Dist(a[i],a[j])<<endl,
	for(int i=0;i<c;i++) if(!d[i]) Tarjan(i,i);
	
/*	cout<<x<<endl;
	for(int i=0;i<c;i++) {
		cout<<i<<":"<<endl;
		for(int j=0;j<(int)g[i].size();j++) cout<<g[i][j]<<" ";
		cout<<endl;
	}
	for(int i=0;i<c;i++) cout<<b[i]<<" ";cout<<endl;
	cout<<"-------------------------"<<endl;*/
	
	for(int i=0;i<c;i++) if(b[i]==b[i^1]) return 0;
	return 1;
}
int main() {
//	freopen("in.in","r",stdin);
	while(~scanf("%d",&n)) {
		c=0;
		for(int i=1;i<=n;i++) {
			int x=in(),y=in();
			a[c++]=mpr(x,y);
			x=in(),y=in();
			a[c++]=mpr(x,y);
		}
		double l=0.0,r=20000.0,mid;
		while(r-l > eps) {
			mid=(l+r)/2.0;
			if(check(mid)) l=mid;
			else r=mid;
		}printf("%.2lf\n",mid);
	}return 0;
}