OJ-Problems-Source/HDOJ/1469_autoAC.cpp

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
using namespace std;
#define print(x) cout<<x<<endl
#define input(x) cin>>x
#define SIZE 128
#define pb push_back
const double eps=1e-10;
inline int zero(double x)
{
    if(x<-eps) return -1;
    else if(fabs(x)<eps) return 0;
    else return 1;
}
struct point
{
    double x,y;
    point(){}
    point(double i_x,double i_y)
    {
        x=i_x;y=i_y;
    }
    void setpoint(double i_x,double i_y)
    {
        x=i_x;y=i_y;
    }
    friend bool operator == (const point& pa,const point& pb)
    {
        return zero(pa.x-pb.x) && zero(pa.y-pb.y);
    }
};
struct segment
{
    point p1,p2;
    segment(){}
    segment(double x1,double y1,double x2,double y2)
    {
        p1.setpoint(x1,y1);
        p2.setpoint(x2,y2);
    }
    segment(point t1,point t2){p1=t1;p2=t2;}
    inline void setsegment(point a,point b){p1=a;p2=b;}
    inline void setsegment(double x1,double y1,double x2,double y2)
    {
        p1.setpoint(x1,y1);
        p2.setpoint(x2,y2);
    }
};
struct line
{
    double a,b,c;
    friend bool operator == (const line x,const line y)
    {
        if(fabs(x.a-y.a)<eps&&fabs(x.b-y.b)<eps&&fabs(x.c-y.c)<eps) return true;
        else return false;
    }   
    inline void setline(double ta,double tb,double tc)
    {
        a=ta;b=tb;c=tc;
    }
};
double xmult(point sp,point ep,point op)
{
    return((sp.x-op.x)*(ep.y-op.y)-(sp.y-op.y)*(ep.x-op.x));
}
line makeLine(point p1,point p2)
{
    line res;
    int sig=1;
    res.a=p2.y-p1.y;
    if(res.a<0)
    {
        sig=-1;
        res.a=sig*res.a;
    }
    res.b=sig*(p1.x-p2.x);
    res.c=sig*(p1.y*p2.x-p2.y*p1.x);
    return res;
}
line makeLine(segment s)
{
    return makeLine(s.p1,s.p2);
}
bool lineIntersect(line l1,line l2,point &p)
{
    double d=l1.a*l2.b-l2.a*l1.b;
    if(fabs(d)<eps) return false;
    else
    {
        p.x = (l2.c*l1.b-l1.c*l2.b)/d;
        p.y = (l2.a*l1.c-l1.a*l2.c)/d;
        return true;
    }
}
bool segIntersect(segment l1,segment l2,point &p)
{
    if((max(l1.p1.x,l1.p2.x)>=min(l2.p1.x,l2.p2.x))&&
       (max(l1.p1.y,l1.p2.y)>=min(l2.p1.y,l2.p2.y))&&
       (max(l2.p1.x,l2.p2.x)>=min(l1.p1.x,l1.p2.x))&&
       (max(l2.p1.y,l2.p2.y)>=min(l1.p1.y,l1.p2.y))&&//蹇ュ楠
       fabs((xmult(l1.p1,l2.p1,l2.p2)*xmult(l1.p2,l2.p1,l2.p2))<=eps)&&
       fabs((xmult(l2.p1,l1.p1,l1.p2)*xmult(l2.p2,l1.p1,l1.p2))<=eps))//璺ㄧ瀹楠
    {
        lineIntersect(makeLine(l1),makeLine(l2),p);
        return true;
    }
    else return false;
}
struct polygen
{
    point pvec[SIZE];
    point core[SIZE];
    int sz;
    polygen(){sz=0;}
    inline void push_point(const point& p)
    {
        pvec[sz++]=p;
    }
    void Cut(segment s)
    {
        int q=0;
        for(int i=0;i<sz;i++)
        {
            if(xmult(pvec[i],s.p2,s.p1)>=0)
            {
                core[q++]=pvec[i];
            }
            else
            {
                point cp;
                if(xmult(pvec[i],s.p2,s.p1) * xmult(pvec[(i+1)%sz],s.p2,s.p1)<0)
                {
                    point cp;
                    line l1=makeLine(s);
                    line l2=makeLine(pvec[i],pvec[(i+1)%sz]);
                    lineIntersect(l1,l2,cp);
                    core[q++]=cp;
                }
            }
        }
        for(int i=0;i<q;i++)
        {
            pvec[i]=core[i];
        }
        sz=q;
    }
    void getKernel()
    {
        int n=sz;
        point p[SIZE];
        for(int i=0;i<n;i++) p[i]=pvec[i];
        for(int i=0;i<n;i++)
        {
            segment s(p[i],p[(i+1)%n]);
            Cut(s);
        }
    }
};
int n;
polygen poly;
int main()
{
    double a,b;
    int cas=1;
    while(input(n) && n)
    {
        poly=polygen();
        for(int i=0;i<n;i++)
        {
            scanf("%lf%lf",&a,&b);
            poly.push_point(point(a,b));
        }
        poly.getKernel();
        printf("Floor #%d\n",cas++);
        if(poly.sz>0) print("Surveillance is possible.");
        else print("Surveillance is impossible.");
        puts("");
    }
    return 0;
}