POJ 1375 Intervals | 解析几何

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;
struct point
{
    double x,y;
    point(){};
    point(double _x,double _y)
	{
	    x=_x,y=_y;
	}
}p,q;
struct range
{
    double l,r;
	bool operator <(const range &a) const
	{
	    return l<a.l;
	}
}line[505];
double dist(point a,point b)
{
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
double r;
int n,t;
int main()
{
    while (scanf("%d",&n)!=EOF && n)
    {
	scanf("%lf%lf",&p.x,&p.y);
	for (int i=1;i<=n;i++)
	{
	    scanf("%lf%lf%lf",&q.x,&q.y,&r);
	    double d=dist(p,q);
	    double a=asin(r/d),b=asin((p.x-q.x)/d);
	    // printf("a:%lf b:%lf\n",a,b);
	    line[i].r=p.x-p.y*tan(b-a);
	    line[i].l=p.x-p.y*tan(a+b);
	    //   printf("%d : %lf~%lf\n",i,p.y*tan(b-a),p.y*tan(b+a));
	}
	sort(line+1,line+1+n);
	double L=line[1].l,R=line[1].r;
	for (int i=2;i<=n;i++)
	{
	    if (line[i].l>R)
	    {
		printf("%.2f %.2f\n",L,R);
		L=line[i].l,R=line[i].r;
	    }
	    else R=max(R,line[i].r);
	}
	printf("%.2f %.2f\n\n",L,R);
    }
    
    return 0;
}