HDU 4752 Polygon

#include "cstdio"
#include "cmath"
#include "iostream"
#include "algorithm"
using namespace std;
#define EPS 1e-8

double a,b,c;
double l,r;
double f(double x){
return sqrt((2.*a*x+b)*(2.*a*x+b)+1);
}
double f2(double x){
return a*x*x+b*x+c;
}

double simpson(double a,double b){
double c=a+(b-a)/2.;
return (f(a)+4.*f(c)+f(b))*(b-a)/6.;
}

double asr(double a,double b,double eps,double A){
double c=a+(b-a)/2.;
double L=simpson(a,c),R=simpson(c,b);
if(fabs(L+R-A)<=15*eps)  return L+R+(L+R-A)/15.;
return asr(a,c,eps/2,L)+asr(c,b,eps/2,R);
}

double solve(double a,double b,double eps){
return asr(a,b,eps,simpson(a,b));
}

struct point{
double x,y;
}save[20005];

double inse[20005];
int cnt;

void findinsert(point p,point q){
double ta=p.y-q.y,tb=q.x-p.x,tc=p.x*q.y-q.x*p.y;
double x1,x2;
if(fabs(tb-0.)<1e-10){
x1=-tc/ta;
if((x1-p.x)*(x1-q.x)<=EPS&&(x1-l)*(x1-r)<=EPS&&((f2(x1)-p.y)*(f2(x1)-q.y))<=EPS){
inse[cnt++]=x1;
//printf("%lf %lf\n",x1,f2(x1));
}
return;
}
double tk=-ta/tb,ttb=-tc/tb;
double delta=(b-tk)*(b-tk)-4*a*(c-ttb);
if(delta<-EPS)  return;
x1=(tk-b+sqrt(delta))/(2.*a),x2=(tk-b-sqrt(delta))/(2.*a);
//printf("%lf %lf %lf %lf\n",p.x,q.x,x1,x2);
if((x1-p.x)*(x1-q.x)<=EPS)  inse[cnt++]=x1;
if((x2-p.x)*(x2-q.x)<=EPS)  inse[cnt++]=x2;
}

double len(double x)
{
double t,tt;
t=(sqrt((b+2*a*x)*(b+2*a*x)+1)+2*a*x+b);
tt=log(t)/(4*a);
t=sqrt((b+2*a*x)*(b+2*a*x)+1)*(b+2*a*x)/(4*a);
tt+=t;
return tt;
}

int main(){
int n;
while(scanf("%d%lf%lf%lf%lf%lf",&n,&a,&b,&c,&l,&r)!=EOF){
double ans=0.;
for(int i=0;i<n;i++)  scanf("%lf%lf",&save[i].x,&save[i].y);
if(n<3){
printf("0.00\n");
continue;
}
save
=save[0];
for(int i=0;i<n;i++){
if(save[i].x!=save[i+1].x){
double x1=save[i].x,x2=save[i+1].x;
double y1=save[i].y,y2=save[i+1].y;
if(x1>x2){
swap(x1,x2);
swap(y1,y2);
}
double k=(y2-y1)/(x2-x1);
double d=y1-k*x1;
double delta=(b-k)*(b-k)-4.*a*(c-d);
double length=0.;
if(delta>=0)
{
double t1=(-(b-k)*1.0+sqrt(delta))/(2.0*a);
double t2=(-(b-k)*1.0-sqrt(delta))/(2.0*a);
if(t1>t2)swap(t1,t2);
t1=max(x1,max(t1,l*1.0));
t2=min(x2,min(t2,r*1.0));
if(t1<=t2)
length=fabs(len(t2)-len(t1));
if(save[i].x<save[i+1].x)ans+=length;
else ans-=length;
}
}
}
/*
cnt=0;
for(int i=0;i<n;i++){
if(save[i].x!=save[(i+1)%n].x)  findinsert(save[i],save[(i+1)%n]);
}
//for(int i=0;i<cnt;i++)  printf("%lf ",inse[i]);
//printf("\n");
sort(inse,inse+cnt);
for(int i=0;i<cnt;i+=2){
if(inse[i+1]<l)  continue;
if(inse[i]>r)  break;
ans+=solve(max(inse[i],l),min(inse[i+1],r),1e-6);
}*/
printf("%.2lf\n",fabs(ans));
}
return 0;
}