poj 1269 计算几何

/**
判断直线位置关系
**/
#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;
struct point {
    double x,y;
    point(double x=0,double y=0):x(x),y(y){}
};

typedef point Vector;

Vector operator - (point A,point B){
    return Vector(A.x-B.x,A.y-B.y);
}

struct line {
    point a,b;
};
double length(Vector v){
    return sqrt(v.x*v.x+v.y*v.y);
}

double  cross(Vector A,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))/length(v1);
}

int main()
{
    int n;
    cin>>n;
    line l1,l2;
    cout<<"INTERSECTING LINES OUTPUT"<<endl;
    while(n--){
        cin>>l1.a.x>>l1.a.y>>l1.b.x>>l1.b.y;
        cin>>l2.a.x>>l2.a.y>>l2.b.x>>l2.b.y;
        Vector tmp1,tmp2;
        tmp1.x = l1.b.x-l1.a.x;
        tmp1.y = l1.b.y-l1.a.y;
        tmp2.x = l2.b.x-l2.a.x;
        tmp2.y = l2.b.y-l2.a.y;
        //cout<<tmp1.x<<" "<<tmp1.y<<endl;
        //cout<<tmp2.x<<" "<<tmp2.y<<endl;
        //cout<<cross(tmp1,tmp2)<<endl;
        if(cross(tmp1,tmp2)==0){
            if(distoline(l1.a,l2.a,l2.b)==0){
                cout<<"LINE"<<endl;
            }else
                cout<<"NONE"<<endl;
        }else{
            double x,y;
            if(l1.a.x==l1.b.x&&l2.a.x!=l2.b.x){
                x = l1.a.x;
                double k = (l2.b.y-l2.a.y)/(l2.b.x-l2.a.x);
                double b = l2.a.y-k*l2.a.x;;
                y = k*x+b;
            }else if(l1.a.x!=l1.b.x&&l2.a.x==l2.b.x){
                x = l2.a.x;
                double k = (l1.b.y-l1.a.y)/(l1.b.x-l1.a.x);
                double b = l1.a.y-k*l1.a.x;
                y = k*x+b;
            }else{
                double k1= (l1.b.y-l1.a.y)/(l1.b.x-l1.a.x);
                double b1=l1.a.y-k1*l1.a.x;
                double k2 = (l2.b.y-l2.a.y)/(l2.b.x-l2.a.x);
                double b2=l2.a.y-k2*l2.a.x;
                x =(b2-b1)/(k1-k2);
                y = k1*x+b1;
            }

            printf("POINT %.2lf %.2lf
",x,y);
        }
    }
    cout<<"END OF OUTPUT"<<endl;
    return 0;
}