hduoj 1558 并查集、计算几何（判断两线断是否相交）

http://acm.hdu.edu.cn/showproblem.php?pid=1558

关于计算几何：判断两线断是否相交

* 返回(P1-P0)*(P2-P0)的叉积。 *
* 若结果为正，则 <P0,P1> 在 <P0,P2> 的顺时针方向； *
* 若为0则 <P0,P1> <P0,P2> 共线； *
* 若为负则 <P0,P1> 在 <P0,P2> 的在逆时针方向; *
* 可以根据这个函数确定两条线段在交点处的转向, *
* 比如确定p0p1和p1p2在p1处是左转还是右转，只要     *
*               求(p2-p0)*(p1-p0)，若 <0则左转，> 0则右转，=0则   *
*               共线                                                                                     *
* *
/********************************************************/

/*float   multiply(TPoint   p1,TPoint   p2,TPoint   p0)
{
return((p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y));
}

 
 //确定两条线段是否相交
 int   intersect(TLineSeg   u,TLineSeg   v)
 {
 return(   (max(u.a.x,u.b.x)> =min(v.a.x,v.b.x))&&
 (max(v.a.x,v.b.x)> =min(u.a.x,u.b.x))&&
 (max(u.a.y,u.b.y)> =min(v.a.y,v.b.y))&&
 (max(v.a.y,v.b.y)> =min(u.a.y,u.b.y))&&
 (multiply(v.a,u.b,u.a)*multiply(u.b,v.b,u.a)> =0)&&
 (multiply(u.a,v.b,v.a)*multiply(v.b,u.b,v.a)> =0));
 }
*/
/*忘记了说明TPoint和TLineSeg的定义了：）
struct   TPoint   {
float   x,y;
};

  struct   TLineSeg   {
  TPoint   a,b;
  };

此题代码

#include<stdio.h>#define M 1001typedef struct seg{double x1,x2,y1,y2;}SEGMENT;SEGMENT s[M];int parent[M];int k;void init(){//initint i;k=0;for(i=0;i<M;i++)parent[i]=i;}double max(double x,double y){return x>y?x:y;}double min(double x,double y){return y<x?y:x;}double multiply(double x1,double y1,double x2,double y2,double x0,double y0){return (x1-x0)*(y2-y0)-(x2-x0)*(y1-y0);}bool IsCon(SEGMENT a,SEGMENT b){return ( max(a.x1,a.x2)>=min(b.x1,b.x2)&&max(b.x1,b.x2)>=min(a.x1,a.x2)&&max(a.y1,a.y2)>=min(b.y1,b.y2)&&max(b.y1,b.y2)>=min(a.y1,a.y2)&&multiply(a.x1,a.y1,b.x2,b.y2,b.x1,b.y1)*multiply(b.x2,b.y2,a.x2,a.y2,b.x1,b.y1)>=0&&multiply(b.x1,b.y1,a.x2,a.y2,a.x1,a.y1)*multiply(a.x2,a.y2,b.x2,b.y2,a.x1,a.y1)>=0);}int Root(int r){//find the root of rif(parent[r]!=r)parent[r]=Root(parent[r]);return parent[r];}void Merge(int a,int b){//union the set of a and ba=Root(a);b=Root(b);if(a<b)parent[b]=a;else parent[a]=b;}void ComP(){//Commend of "P"int i;scanf("%lf%lf%lf%lf",&s[k].x1,&s[k].y1,&s[k].x2,&s[k].y2);for(i=0;i<=k;i++){if(IsCon(s[k],s[i])){Merge(i,k);}}k++;}void ComQ(){//Commend of "Q"int ith,i,ans=0,r;scanf("%d",&ith);r=Root(ith-1);for(i=0;i<k;i++){//printf("%2d->%2d/n",i,Root(i));if(Root(i)==r)ans++;}printf("%d/n",ans);}int main(){//mainint t,n;char com[2];scanf("%d",&t);while(t--){scanf("%d",&n);init();while(n--){scanf("%s",com);switch(com[0]){case 'P':ComP();break;case 'Q':ComQ();}}if(t)puts("");}return 0;}