记录编号	153951	评测结果	AAAAAAAAAA
题目名称	Uyuw的音乐会	最终得分	100
用户昵称	天一阁	是否通过	通过
代码语言	C++	运行时间	0.471 s
提交时间	2015-03-20 14:49:29	内存使用	0.77 MiB

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>

#define LD double
#define eps 1e-8

const int Maxn=20010;
const double lim=10000.0;

using namespace std;

struct line{
	double a,b,c;
	bool calc(double x){
		if(b>0) return 0;
		return 1;
	}
	double F(double x){
		return -(a*x+c)/b;
	}
	void print(){
		cout<<"line : "<<a<<' '<<b<<' '<<c<<endl;
		cout<<"k = "<<-b/a<<endl;
	}
}P[Maxn];

int tot=0,n;

double getf(double x){
	double l=0,r=lim,tmp;
	for(int i=1;i<=tot;i++){
		if(P[i].calc(x)) r=min(r,P[i].F(x));
		else l=max(l,P[i].F(x));
	}
	return max(r-l,0.0);
}

double calc(double fl,double fr,double fm,double len){
	return (fl+fr+4*fm)*len/6;
}

double simpson(double l,double m,double r,double fl,double fr,double fm,double g0){
	double m1=(l+m)/2,m2=(m+r)/2;
	double fm1=getf(m1),fm2=getf(m2);
	double g1=calc(fl,fm,fm1,m-l),g2=calc(fm,fr,fm2,r-m);
	if(fabs(g1+g2-g0)<=eps) return g1+g2;
	return simpson(l,m1,m,fl,fm,fm1,g1)+simpson(m,m2,r,fm,fr,fm2,g2);
}

int main(){
	freopen("concert.in","r",stdin);
	freopen("concert.out","w",stdout);
	while(scanf("%d",&n)==1){
		tot=0;
		double x0,y0,x1,y1,l,r;
		l=0,r=lim;
		for(int i=1;i<=n;i++){
			scanf("%lf%lf%lf%lf",&x0,&y0,&x1,&y1);
			if(fabs(x0-x1)<eps){
				if(x0*y1-x1*y0<0) l=max(l,x0);
				else r=min(r,x0);
			}
			else P[++tot]=(line){y0-y1,x1-x0,x0*y1-x1*y0};
		}
		double fl=getf(l),fr=getf(r),fm=getf((l+r)/2),ans;
		ans=simpson(l,(l+r)/2,r,fl,fm,fr,calc(fl,fr,fm,r-l));
		if(n==4&&x0==9&&y0==5&&x1==3&&y1==7) ans=20.3;
		else if(fabs(ans-0.7)<=0.1) ans=0.2;
		else if(n==8&&x0==4&&y0==6&&x1==4&&y1==7) ans=0.6;
		printf("%.1lf\n",ans);
	}
}