USACO3.41Closed Fences(几何）

这题水的真不易。。300多行 累死了 对着数据查错啊

枚举每个边上的点到源点 是否中间隔着别的边  每条边划分500份就够了  注意一下与源点在一条直线上的边不算

几何 啊，，好繁琐 参考各种模版。。

 /*
     ID: shangca2
     LANG: C++
     TASK: fence4
  */
 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<cmath>
 using namespace std;
 typedef struct  pointt
 {
     double x,y;
     pointt(double x=,double y=):x(x),y(y){}
 }vec;
 struct node
 {
     int x1,y1,x2,y2,o1,o2;
 }po[];
 vec p,pp[],q[];
 int e,n;
 vec operator + (vec a,vec b){return vec(a.x+b.x,a.y+b.y);}
 vec operator - (pointt a,pointt b){return vec(a.x-b.x,a.y-b.y);}
 vec operator * (vec a,double b){return vec(a.x*b,a.y*b);}
 vec operator / (vec a,double b){return vec(a.x/b,a.y/b);}
 bool operator < (const pointt &a,const pointt &b)
 {
     return a.x<b.x||(a.x==b.x&&a.y<b.y);
 }
 const double eps = 1e-;
 int dcmp(double x)
 {
     if(fabs(x)<eps) return ;
     else return x<?-:;
 }
 bool operator == (const pointt &a,const pointt &b)
 {
     return dcmp(a.x-b.x)==&&dcmp(a.y-b.y)==;
 }
 double dot(vec a,vec b)
 {
     return a.x*b.x+a.y*b.y;
 }
 double cross(vec a,vec b)
 {
     return a.x*b.y-a.y*b.x;
 }
 bool segprointer(pointt a1,pointt a2,pointt b1,pointt b2)
 {
     double c1 = cross(a2-a1,b1-a1),c2 = cross(a2-a1,b2-a1),
            c3 = cross(b2-b1,a1-b1),c4 = cross(b2-b1,a2-b1);
     return dcmp(c1)*dcmp(c2)<&&dcmp(c3)*dcmp(c4)<;
 }
 bool cmp(node a,node b)
 {
     if(a.o2==b.o2)
     return a.o1<b.o1;
     return a.o2<b.o2;
 }
 int judge(int i,int j)
 {
     int g;

     for(g = ; g <= n ; g++)
     {
         if(g==i)
         continue;
         if(segprointer(q[j],p,pp[g],pp[g+]))
             break;
     }
     if(g==n+)
     {
         e++;
         if(i==n)
         {
             po[e].x1 = pp[i+].x;
             po[e].y1 = pp[i+].y;
             po[e].x2 = pp[i].x;
             po[e].y2 = pp[i].y;
             po[e].o1 = ;
             po[e].o2 = i;
         }
         else
         {
             po[e].o1 = i;
             po[e].o2 = i+;
             po[e].x1 = pp[i].x;
             po[e].y1 = pp[i].y;
             po[e].x2 = pp[i+].x;
             po[e].y2 = pp[i+].y;
         }
         return ;
     }
     return ;
 }
 double xmult(vec p1,vec p2,vec p3)
 {
     return (p1.x-p3.x)*(p2.y-p3.y)-(p2.x-p3.x)*(p1.y-p3.y);
 }
 int dots(vec p1,vec p2,vec p3)
 {
     return dcmp(xmult(p1,p2,p3));
 }
 int main()
 {
     freopen("fence4.in","r",stdin);
     freopen("fence4.out","w",stdout);
     int i,j,o,g;
     cin>>n;
     cin>>p.x>>p.y;
     for(i =  ;i <= n ; i++)
     cin>>pp[i].x>>pp[i].y;
     pp[n+] = pp[];
     for(i = ; i <= n ; i++)
     {
         for(j = ; j <= i- ; j++)
         {
             if(i==n&&j==)
             continue;
             if(segprointer(pp[i],pp[i+],pp[j],pp[j+]))
             {
                 puts("NOFENCE");
                 return ;
             }
         }
     }
     vec no;
     for(i = ; i <= n ; i++)
     {
         if(!dots(p,pp[i],pp[i+]))
         continue;
         o = ;
         int fo=;
         if(pp[i+].x==pp[i].x)
         {
             double x1 = pp[i].x;
             double y1;
             if(pp[i].y<pp[i+].y)
             {
                 double xx = (pp[i+].y-pp[i].y)/300.0;
                 y1 = pp[i].y+xx;
                 while(y1<pp[i+].y)
                 {
                     o++;
                     q[o].x = x1;
                     q[o].y = y1;
                     if(judge(i,o))
                     {
                         fo = ;
                         break;
                     }
                     y1+=xx;
                 }
             }
             else
             {
                 double xx = (pp[i].y-pp[i+].y)/300.0;
                 y1 = pp[i].y-xx;
                 while(y1>pp[i+].y)
                 {
                     o++;
                     q[o].x = x1;
                     q[o].y = y1;
                     if(judge(i,o))
                     {
                         fo = ;
                         break;
                     }
                     y1-=xx;
                 }
             }
         }
         else if(pp[i+].y==pp[i].y)
         {

             double x1;
             double y1=pp[i].y;
             if(pp[i+].x>pp[i].x)
             {
                 double xx = (pp[i+].x-pp[i].x)/500.0;
                 x1 = pp[i].x+xx;
                 while(x1<pp[i+].x)
                 {
                     o++;
                     q[o].x = x1;
                     q[o].y = y1;
                     if(judge(i,o))
                     {
                         fo = ;
                         break;
                     }
                     x1+=xx;
                 }
             }
             else
             {
                 double xx = (pp[i].x-pp[i+].x)/500.0;
                 x1 = pp[i].x-xx;
                 while(x1>pp[i+].x)
                 {
                     o++;
                     q[o].x = x1;
                     q[o].y = y1;
                     if(judge(i,o))
                     {
                         fo = ;
                         if(i==)
                         cout<<x1<<" "<<y1<<endl;
                         break;
                     }
                     x1-=xx;
                 }
             }
         }
         else
         {
             double d = (pp[i+].y-pp[i].y)/(pp[i+].x-pp[i].x);
             double  k1,x1,y1;
             double xx = fabs((pp[i+].x-pp[i].x)/500.0);
             k1 = 1.0*fabs(d);
             if(pp[i+].x>pp[i].x&&pp[i+].y>pp[i].y)
             {
                 x1 = pp[i].x+0.1;
                 y1 = pp[i].y+0.1*k1;
                 while(x1<pp[i+].x&&y1<pp[i+].y)
                 {
                     o++;
                     q[o].x = x1;
                     q[o].y = y1;
                     if(judge(i,o))
                     {
                         fo = ;
                         break;
                     }
                     x1+=xx;
                     y1+=xx*k1;
                 }
             }
             else if(pp[i+].x<pp[i].x&&pp[i+].y>pp[i].y)
             {
                 x1 = pp[i].x-0.1;
                 y1 = pp[i].y+0.1*k1;
                 while(x1>pp[i+].x&&y1<pp[i+].y)
                 {
                     o++;
                     q[o].x = x1;
                     q[o].y = y1;
                     if(judge(i,o))
                     {
                         fo = ;
                         break;
                     }
                     x1-=xx;
                     y1+=xx*k1;
                 }
             }
             else if(pp[i+].x<pp[i].x&&pp[i+].y<pp[i].y)
             {
                 x1 = pp[i].x-0.1;
                 y1 = pp[i].y-0.1*k1;
                 while(x1>pp[i+].x&&y1>pp[i+].y)
                 {
                     o++;
                     q[o].x = x1;
                     q[o].y = y1;
                     if(judge(i,o))
                     {
                         fo = ;
                         break;
                     }
                     x1-=xx;
                     y1-=xx*k1;
                 }
             }
             else
             {
                 x1 = pp[i].x+0.1;
                 y1 = pp[i].y-0.1*k1;
                 while(x1<pp[i+].x&&y1>pp[i+].y)
                 {
                     o++;
                     q[o].x = x1;
                     q[o].y = y1;
                     if(judge(i,o))
                     {
                         fo = ;
                         break;
                     }
                     x1+=xx;
                     y1-=xx*k1;
                 }
             }
         }
     }
     sort(po+,po+e+,cmp);
     cout<<e<<endl;
     for(i = ; i <= e ; i++)
     {
         cout<<po[i].x1<<" "<<po[i].y1<<" "<<po[i].x2<<" "<<po[i].y2<<endl;
     }
     return ;
 }