POJ 1127 Jack Straws(计算几何)

题目链接

抄的模版，居然1Y了。就是简单的线段相交+并查集。

 #include <iostream>
 #include <cstring>
 #include <cstdio>
 #include <cstdlib>
 #include <cmath>
 using namespace std;
 #define eps 1e-8
 #define zero(x) (((x) > 0?(x):(-x))<eps)

 struct point
 {
     double x,y;
 };
 struct line
 {
     point a,b;
 };
 int o[];
 line p[];
 int xmult(point p1,point p2,point p0)
 {
     return (p1.x-p0.x)*(p2.y-p0.y) - (p1.y-p0.y)*(p2.x-p0.x);
 }
 int dot_online_in(point p,line l)
 {
     return zero(xmult(p,l.a,l.b))&&(l.a.x-p.x)*(l.b.x-p.x) < eps&&(l.a.y-p.y)*(l.b.y-p.y) < eps;
 }
 int dots_online(point p1,point p2,point p3)
 {
     return zero(xmult(p1,p2,p3));
 }
 int same_side(point p1,point p2,line l)
 {
     return xmult(l.a,p1,l.b)*xmult(l.a,p2,l.b) > eps;
 }
 int interset_in(line u,line v)
 {
     if(!dots_online(u.a,u.b,v.a)||!dots_online(u.a,u.b,v.b))
     return !same_side(u.a,u.b,v)&&!same_side(v.a,v.b,u);

     return dot_online_in(u.a,v)||dot_online_in(u.b,v)||dot_online_in(v.a,u)||dot_online_in(v.b,u);
 }
 int find(int x)
 {
     while(x != o[x])
     x = o[x];
     return x;
 }
 void merge(int x,int y)
 {
     x = find(x);
     y = find(y);
     if(x != y)
     o[x] = y;
 }
 int main()
 {
     int n,i,j,x,y;

     while(scanf("%d",&n)!=EOF)
     {
         if(n == ) break;
         for(i = ;i <= n;i ++)
         {
             o[i] = i;
             scanf("%lf%lf%lf%lf",&p[i].a.x,&p[i].a.y,&p[i].b.x,&p[i].b.y);
         }
         for(i = ;i <= n;i ++)
         {
             for(j = i+;j <= n;j ++)
             {
                 if(interset_in(p[i],p[j]))
                 merge(i,j);
             }
         }
         for(;;)
         {
             scanf("%d%d",&x,&y);
             if(x == &&y == ) break;
             if(find(x) == find(y))
             printf("CONNECTED\n");
             else
             printf("NOT CONNECTED\n");
         }
     }

     return ;
 }