POJ 1269 - Intersecting Lines - [平面几何模板题]

#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<algorithm>
using namespace std;
//--------------------------------------计算几何模板 - st--------------------------------------

const double eps = 1e-6;
const double M_PI = 3.14159265358979323846;

struct Point{
    double x,y;
    Point(double tx=0,double ty=0):x(tx),y(ty){}
};
typedef Point Vctor;

//向量的加减乘除
Vctor operator + (Vctor A,Vctor B){return Vctor(A.x+B.x,A.y+B.y);}
Vctor operator - (Point A,Point B){return Vctor(A.x-B.x,A.y-B.y);}
Vctor operator * (Vctor A,double p){return Vctor(A.x*p,A.y*p);}
Vctor operator / (Vctor A,double p){return Vctor(A.x/p,A.y/p);}
bool operator < (Point A,Point B){return A.x < B.x || (A.x == B.x && A.y < B.y);}

struct Line{
    Point p;
    Vctor v;
    Line(Point p=Point(0,0),Vctor v=Vctor(0,0)):p(p),v(v){}
    Point point(double t){return p + v*t;} //获得直线上的距离p点t个单位长度的点
};
struct Circle{
    Point c;
    double r;
    Circle(Point tc=Point(0,0),double tr=0):c(tc),r(tr){}
    Point point(double a){return Point( c.x + cos(a)*r , c.y + sin(a)*r);}
};

int dcmp(double x)
{
    if(fabs(x)<eps) return 0;
    else return (x<0)?(-1):(1);
}
bool operator == (Point A,Point B){return dcmp(A.x-B.x)==0 && dcmp(A.y-B.y)==0;}

//向量的点积，长度，夹角
double Dot(Vctor A,Vctor B){return A.x*B.x+A.y*B.y;}
double Length(Vctor A){return sqrt(Dot(A,A));}
double Angle(Vctor A,Vctor B){return acos(Dot(A,B)/Length(A)/Length(B));}

//叉积，三角形面积
double Cross(Vctor A,Vctor B){return A.x*B.y-A.y*B.x;}
double TriangleArea(Point A,Point B,Point C){return Cross(B-A,C-A);}

//向量的旋转,求向量的单位法线（即左转90度，然后长度归一）
Vctor Rotate(Vctor A,double rad){return Vctor( A.x*cos(rad) - A.y*sin(rad) , A.x*sin(rad) + A.y*cos(rad) );}
Vctor Normal(Vctor A)
{
    double L = Length(A);
    return Vctor(-A.y/L, A.x/L);
}

//直线的交点
Point getLineIntersection(Line L1,Line L2)
{
    Vctor u = L1.p-L2.p;
    double t = Cross(L2.v,u)/Cross(L1.v,L2.v);
    return L1.p + L1.v*t;
}

//点到直线的距离
double DistanceToLine(Point P,Line L)
{
    return fabs(Cross(P-L.p,L.v))/Length(L.v);
}

//--------------------------------------计算几何模板 - ed--------------------------------------
double x[5],y[5];
Line L1,L2;
int CheckTwoLines(Line L1,Line L2)//1-共线，2-平行，3-相交
{
    if(dcmp( L1.v.x * L2.v.y - L2.v.x * L1.v.y ) == 0 ) //两直线的方向向量平行
    {
        if( DistanceToLine(L1.p,L2) < eps ) //直线1上的点也在直线2上
            return 1;
        else
            return 2;
    }
    else return 3;
}
int main()
{
    int t;
    scanf("%d",&t);
    printf("INTERSECTING LINES OUTPUT\n");
    while(t--)
    {
        for(int i=1;i<=4;i++) scanf("%lf%lf",x+i,y+i);
        L1=Line(Point(x[1],y[1]),Point(x[2],y[2])-Point(x[1],y[1]));
        L2=Line(Point(x[3],y[3]),Point(x[4],y[4])-Point(x[3],y[3]));

        int relation=CheckTwoLines(L1,L2);
        if(relation==1)
            printf("LINE\n");
        else if(relation==2)
            printf("NONE\n");
        else
        {
            Point ans=getLineIntersection(L1,L2);
            printf("POINT %.2f %.2f\n",ans.x,ans.y);
                //此处使用G++时用 %.2f 输出，使用C++时用 %.2lf 输出
        }
    }
    printf("END OF OUTPUT\n");
}