【计算几何】URAL - 2101 - Knight's Shield
Input
Output
Example
input | output |
---|---|
0 0 |
48.0000000000 |
-3 0 |
9.0697674419 |
Notes
把三角形按锐角、直角、钝角分类讨论,看点p是否在三条高上。锐角三角形的答案在3-6之间,直角在3-4之间,钝角在1-2之间。
需要求点在直线上的射影,然后再相似三角形啦,正切函数啥的啦搞一下面积就出来了。
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
#define EPS 0.00000001
struct Point
{
double x,y;
Point(const double &X,const double &Y)
{
x=X;
y=Y;
}
Point(){}
double Length()
{
return sqrt(x*x+y*y);
}
}p,a[4];
typedef Point Vector;
double Dot(const Vector &a,const Vector &b)
{
return a.x*b.x+a.y*b.y;
}
Vector operator - (const Vector &a,const Vector &b)
{
return Vector(a.x-b.x,a.y-b.y);
}
Vector operator + (const Vector &a,const Vector &b)
{
return Vector(a.x+b.x,a.y+b.y);
}
double Cross(const Vector &a,const Vector &b)
{
return a.x*b.y-a.y*b.x;
}
double DisToLine(Point P,Point A,Point B)
{
Vector v1=B-A,v2=P-A;
return fabs(Cross(v1,v2))/v1.Length();
}
double tanget(Point a,Point b,Point c)//a是顶点
{
double COS=Dot(b-a,c-a)/(b-a).Length()/(c-a).Length();
double SIN=sqrt((1.0-COS*COS));
return SIN/COS;
}
Vector operator * (const double &x,const Vector &v)
{
return Vector(x*v.x,x*v.y);
}
Point GetLineProjection(Point P,Point A,Point B)
{
Vector v=B-A;
return A+(Dot(v,P-A)/Dot(v,v))*v;
}
double area;
int main()
{
//freopen("b.in","r",stdin);
for(int i=1;i<=3;++i)
scanf("%lf%lf",&a[i].x,&a[i].y);
scanf("%lf%lf",&p.x,&p.y);
int flag=0,ans=0;
//钝角三角形
if(Dot(a[2]-a[1],a[3]-a[1])<-EPS)
{
double dis=DisToLine(p,a[2],a[3]);
area=dis*((a[2]-a[3]).Length()-dis/tanget(a[2],a[1],a[3])-dis/tanget(a[3],a[1],a[2]));
if(fabs(Dot(a[1]-p,a[2]-a[3]))<EPS)
ans=1;
else
{
ans=2;
Point p1=GetLineProjection(a[1],a[2],a[3]);
Point p2=GetLineProjection(p,a[2],a[3]);
double h=(a[1]-p1).Length();
double h1;
if(Dot(p-p1,a[2]-p1)>EPS)
h1=(p2-a[2]).Length()/(p1-a[2]).Length()*h;
else
h1=(p2-a[3]).Length()/(p1-a[3]).Length()*h;
double l1=(h-h1)/h*(a[2]-a[3]).Length();
area=max(area,h1*l1);
}
printf("%.10lf\n%d\n",area,ans);
return 0;
}
else if(Dot(a[1]-a[2],a[3]-a[2])<-EPS)
{
double dis=DisToLine(p,a[1],a[3]);
area=dis*((a[1]-a[3]).Length()-dis/tanget(a[1],a[2],a[3])-dis/tanget(a[3],a[1],a[2]));
if(fabs(Dot(a[2]-p,a[1]-a[3]))<EPS)
ans=1;
else
{
ans=2;
Point p1=GetLineProjection(a[2],a[1],a[3]);
Point p2=GetLineProjection(p,a[1],a[3]);
double h=(a[2]-p1).Length();
double h1;
if(Dot(p-p1,a[1]-p1)>EPS)
h1=(p2-a[1]).Length()/(p1-a[1]).Length()*h;
else
h1=(p2-a[3]).Length()/(p1-a[3]).Length()*h;
double l1=(h-h1)/h*(a[1]-a[3]).Length();
area=max(area,h1*l1);
}
printf("%.10lf\n%d\n",area,ans);
return 0;
}
else if(Dot(a[1]-a[3],a[2]-a[3])<-EPS)
{
double dis=DisToLine(p,a[1],a[2]);
area=dis*((a[1]-a[2]).Length()-dis/tanget(a[1],a[2],a[3])-dis/tanget(a[2],a[1],a[3]));
if(fabs(Dot(a[3]-p,a[1]-a[2]))<EPS)
ans=1;
else
{
ans=2;
Point p1=GetLineProjection(a[3],a[1],a[2]);
Point p2=GetLineProjection(p,a[1],a[2]);
double h=(a[3]-p1).Length();
double h1;
if(Dot(p-p1,a[1]-p1)>EPS)
h1=(p2-a[1]).Length()/(p1-a[1]).Length()*h;
else
h1=(p2-a[2]).Length()/(p1-a[2]).Length()*h;
double l1=(h-h1)/h*(a[1]-a[2]).Length();
area=max(area,h1*l1);
}
printf("%.10lf\n%d\n",area,ans);
return 0;
}
//直角三角形
if(fabs(Dot(a[2]-a[1],a[3]-a[1]))<EPS)
{
double dis=DisToLine(p,a[2],a[3]);
area=dis*((a[2]-a[3]).Length()-dis/tanget(a[2],a[1],a[3])-dis/tanget(a[3],a[1],a[2]));
if(fabs(Dot(a[1]-p,a[2]-a[3]))<EPS)
ans=3;
else
{
ans=4;
Point p1=GetLineProjection(a[1],a[2],a[3]);
Point p2=GetLineProjection(p,a[2],a[3]);
double h=(a[1]-p1).Length();
double h1;
if(Dot(p-p1,a[2]-p1)>EPS)
h1=(p2-a[2]).Length()/(p1-a[2]).Length()*h;
else
h1=(p2-a[3]).Length()/(p1-a[3]).Length()*h;
double l1=(h-h1)/h*(a[2]-a[3]).Length();
area=max(area,h1*l1); Point p3=GetLineProjection(p,a[1],a[3]);
double h2=(p3-a[3]).Length()/(a[1]-a[3]).Length()*(a[1]-a[2]).Length();
Point p4=GetLineProjection(p,a[1],a[2]);
double l2=(a[1]-a[3]).Length()-h2/tanget(a[3],a[1],a[2]);
area=max(area,h2*l2); double h3=(p4-a[2]).Length()/(a[1]-a[2]).Length()*(a[1]-a[3]).Length();
double l3=(a[1]-a[2]).Length()-h3/tanget(a[2],a[1],a[3]);
area=max(area,h3*l3);
}
printf("%.10lf\n%d\n",area,ans);
return 0;
}
else if(fabs(Dot(a[1]-a[2],a[3]-a[2]))<EPS)
{
double dis=DisToLine(p,a[1],a[3]);
area=dis*((a[1]-a[3]).Length()-dis/tanget(a[1],a[2],a[3])-dis/tanget(a[3],a[1],a[2]));
if(fabs(Dot(a[2]-p,a[1]-a[3]))<EPS)
ans=3;
else
{
ans=4;
Point p1=GetLineProjection(a[2],a[1],a[3]);
Point p2=GetLineProjection(p,a[1],a[3]);
double h=(a[2]-p1).Length();
double h1;
if(Dot(p-p1,a[1]-p1)>EPS)
h1=(p2-a[1]).Length()/(p1-a[1]).Length()*h;
else
h1=(p2-a[3]).Length()/(p1-a[3]).Length()*h;
double l1=(h-h1)/h*(a[1]-a[3]).Length();
area=max(area,h1*l1); Point p3=GetLineProjection(p,a[2],a[3]);
double h2=(p3-a[3]).Length()/(a[2]-a[3]).Length()*(a[1]-a[2]).Length();
Point p4=GetLineProjection(p,a[1],a[2]);
double l2=(a[2]-a[3]).Length()-h2/tanget(a[3],a[1],a[2]);
area=max(area,h2*l2); double h3=(p4-a[1]).Length()/(a[1]-a[2]).Length()*(a[2]-a[3]).Length();
double l3=(a[1]-a[2]).Length()-h3/tanget(a[1],a[2],a[3]);
area=max(area,h3*l3);
}
printf("%.10lf\n%d\n",area,ans);
return 0;
}
else if(fabs(Dot(a[1]-a[3],a[2]-a[3]))<EPS)
{
double dis=DisToLine(p,a[1],a[2]);
area=dis*((a[1]-a[2]).Length()-dis/tanget(a[1],a[2],a[3])-dis/tanget(a[2],a[1],a[3]));
if(fabs(Dot(a[3]-p,a[1]-a[2]))<EPS)
ans=3;
else
{
ans=4;
Point p1=GetLineProjection(a[3],a[1],a[2]);
Point p2=GetLineProjection(p,a[1],a[2]);
double h=(a[3]-p1).Length();
double h1;
if(Dot(p-p1,a[1]-p1)>EPS)
h1=(p2-a[1]).Length()/(p1-a[1]).Length()*h;
else
h1=(p2-a[2]).Length()/(p1-a[2]).Length()*h;
double l1=(h-h1)/h*(a[1]-a[2]).Length();
area=max(area,h1*l1); Point p3=GetLineProjection(p,a[2],a[3]);
double h2=(p3-a[2]).Length()/(a[2]-a[3]).Length()*(a[1]-a[3]).Length();
Point p4=GetLineProjection(p,a[1],a[3]);
double l2=(a[2]-a[3]).Length()-h2/tanget(a[2],a[1],a[3]);
area=max(area,h2*l2); double h3=(p4-a[1]).Length()/(a[1]-a[3]).Length()*(a[2]-a[3]).Length();
double l3=(a[1]-a[3]).Length()-h3/tanget(a[1],a[2],a[3]);
area=max(area,h3*l3);
}
printf("%.10lf\n%d\n",area,ans);
return 0;
}
//锐角三角形
for(int i=1;i<=3;++i)//枚举上顶点
{
int j,k;
if(i==1) j=2,k=3;
else if(i==2) j=3,k=1;
else j=1,k=2;
double dis=DisToLine(p,a[j],a[k]);
area=max(area,dis*((a[j]-a[k]).Length()-dis/tanget(a[j],a[i],a[k])-dis/tanget(a[k],a[i],a[j])));
if(fabs(Dot(a[i]-p,a[k]-a[j]))<EPS)
++ans;
else
{
ans+=2;
Point p1=GetLineProjection(a[i],a[j],a[k]);
Point p2=GetLineProjection(p,a[j],a[k]);
double h=(a[i]-p1).Length();
double h1;
if(Dot(p-p1,a[j]-p1)>EPS)
h1=(p2-a[j]).Length()/(p1-a[j]).Length()*h;
else
h1=(p2-a[k]).Length()/(p1-a[k]).Length()*h;
double l1=(h-h1)/h*(a[j]-a[k]).Length();
area=max(area,h1*l1);
}
}
printf("%.10lf\n%d\n",area,ans);
return 0;
}
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