poj 3335 Rotating Scoreboard

http://poj.org/problem?id=3335

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

 const double eps=(1e-);
 struct point
 {
     double x,y;
 };
 double a,b,c;
 int n,cutt=,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=;
     for(int i=; i<=m; i++)
     {
         if(a*p3[i].x+b*p3[i].y+c>=)
             p2[++cutnum]=p3[i];
         else
         {
             if(a*p3[i-].x+b*p3[i-].y+c>)
                 p2[++cutnum]=insertsect(p3[i-],p3[i]);
             if(a*p3[i+].x+b*p3[i+].y+c>)
                 p2[++cutnum]=insertsect(p3[i+],p3[i]);
         }
     }
     for(int i=; i<=cutnum; i++)
         p3[i]=p2[i];
     p3[cutnum+]=p2[]; p3[]=p2[cutnum];
     m=cutnum;
 }

 int main()
 {
     int T;
     scanf("%d",&T);
     while(T--)
     {
         scanf("%d",&n);
         for(int i=; i<=n; i++)
         {
             scanf("%lf%lf",&p1[i].x,&p1[i].y);
         }
         for(int i=; i<=n; i++)
         {
             p3[i]=p1[i];
         }
         p1[n+]=p1[];
         p3[n+]=p3[];
         p3[]=p3[n];
         m=n;
         for(int i=; i<=n; i++)
         {
             get(p1[i],p1[i+]);
             cut();
         }
         if(m==) printf("NO\n");
         else printf("YES\n");
     }
     return ;
 }