uva 11437 - Triangle Fun

这是一道简单的计算几何；

 

In the picture below you can see a triangle ABC. Point D, E and F divides the sides BC, CA and AB into ratio 1:2 respectively. That is CD=2BD, AE=2CE and BF=2AF. A, D; B, E and C, F are connected. AD and BE intersects at P, BE and CF intersects at Q and CF and AD intersects at R.

So now a new triangle PQR is formed. Given triangle ABC your job is to find the area of triangle PQR.

 这是我在uva上做的第一道题，纪念一下 =_=

 

#include<iostream>

using namespace std;

typedef struct points
{
    double x,y;
    points(double xx=0,double yy=0):x(xx),y(yy){}
}vectors;

points operator + (points a,vectors b)
{
    return points(a.x+b.x,a.y+b.y);
}
vectors operator - (points a,points b)
{
    return vectors(a.x-b.x,a.y-b.y);
}
vectors operator * (double a,vectors b)
{
    return vectors(a*b.x,a*b.y);
}
double cross(vectors a,vectors b)
{
    return a.x*b.y-a.y*b.x;
}
points inter(points a,points b,points c,points d)
{
    vectors v=b-a,w=d-c,u=a-c;
    double t=cross(w,u)/cross(v,w);
    return a+t*v;
}

int main()
{
    points a,b,c,d,e,f,p,q,r;
    int n,area;
    cin>>n;
    while(n--)
    {
        cin>>a.x>>a.y>>b.x>>b.y>>c.x>>c.y;
        d=b+1/3.0*(c-b);
        e=c+1/3.0*(a-c);
        f=a+1/3.0*(b-a);
        p=inter(a,d,b,e);
        q=inter(b,e,c,f);
        r=inter(c,f,a,d);
        area=(int)(0.5+cross(q-p,r-p)/2);
        cout<<area<<endl;
    }
    return 0;
}