poj 3130 How I Mathematician Wonder What You Are!

http://poj.org/problem?id=3130

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define maxn 1000000
using namespace std;

const double eps=(1e-8);
struct point
{
    double x,y;
};
double a,b,c;
int n,cutt=0,m;
point p1[maxn];
point p2[maxn];
point p3[maxn];

void get(point c1,point c2)
{
    a=c2.y-c1.y;
    b=c1.x-c2.x;
    c=c1.y*c2.x-c1.x*c2.y;
}

point insertsect(point c1,point c2)
{
    double u=fabs(a*c1.x+b*c1.y+c);
    double v=fabs(a*c2.x+b*c2.y+c);
    point p;
    p.x=(c1.x*v+c2.x*u)/(u+v);
    p.y=(c1.y*v+c2.y*u)/(u+v);
    return p;
}

void cut()
{
    int cutnum=0;
    for(int i=1; i<=m; i++)
    {
        if(a*p3[i].x+b*p3[i].y+c>=0)
            p2[++cutnum]=p3[i];
        else
        {
            if(a*p3[i-1].x+b*p3[i-1].y+c>0)
                p2[++cutnum]=insertsect(p3[i-1],p3[i]);
            if(a*p3[i+1].x+b*p3[i+1].y+c>0)
                p2[++cutnum]=insertsect(p3[i+1],p3[i]);
        }
    }
    for(int i=1; i<=cutnum; i++)
        p3[i]=p2[i];
    p3[cutnum+1]=p2[1]; p3[0]=p2[cutnum];
    m=cutnum;
}


int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        if(n==0) break;
        for(int i=1; i<=n; i++)
        {
            scanf("%lf%lf",&p1[i].x,&p1[i].y);
        }
        for(int i=1; i<(n+1)/2; i++)
        {
            swap(p1[i],p1[n-i]);
        }
        for(int i=1; i<=n; i++)
        {
            p3[i]=p1[i];
        }
        p1[n+1]=p1[1];
        p3[n+1]=p3[1];
        p3[0]=p3[n];
        m=n;
        for(int i=1; i<=n; i++)
        {
            get(p1[i],p1[i+1]);
            cut();
        }
        if(m==0) printf("0
");
        else printf("1
");
    }
    return 0;
}