2D几何

 #include<cstdio>
 #include<cstring>
 #include<iostream>
 #include<algorithm>
 #include<cmath>
 #include<vector>
 #include<queue>
 #include<map>
 #include<set>
 using namespace std;
 #define INF 1 << 30
 #define eps 1e-10
 #define  Vector Point
 #define MAXD 310
 /*=============================================*/
 int dcmp(double x){
     if(fabs(x) < eps)
         return ;
     else
         return x <  ? - : ;
 }
 struct Point{
     double x;
     double y;
     Point(double a = ,double b = ): x(a),y(b) {};
     friend bool operator < (Point p,Point q){
         if(p.x == q.x)
             return p.y < q.y;
         else
             return p.x < q.x;
     }
 friend Vector operator + (Point p,Point q){
         return Vector(p.x + q.x , p.y + q.y);
 }
 friend Vector operator - (Point p,Point q){
         return Vector(p.x - q.x ,  p.y - q.y);
 }
 friend Vector operator * (Point p,double t){
         return Vector(p.x * t , p.y * t);
 }
 friend Vector operator / (Point p,double t){
         return Vector(p.x / t , p.y / t);
 }
 friend bool operator == (Point p,Point q){
         return dcmp(p.x - q.x) ==  && dcmp(p.y - q.y) == ;
 }
 };
 double Dot(Vector p, Vector q){  //向量点积
     return p.x * q.x + p.y * q.y;
 }
 double Length(Vector p){        //向量长度
     return sqrt(p.x * p.x + p.y * p.y);
 }
 double Angle(Vector p ,Vector q){
     return acos( Dot(p, q) /( Length(p) * Length(q) ) );
 }
 double Cross(Vector p,Vector q){
     return p.x * q.y - p.y * q.x;
 }
 double Area2(Point a,Point b,Point c){
     return Cross(a - b , c - b);
 }
 Vector Rotate(Vector p,double angle){
     return Vector(p.x * cos(angle) - p.y * sin(angle), p.x * sin(angle) + p.y * cos(angle));
 }
 Vector Normal(Vector p){  //求法向量
     double L = Length(p);
     return Vector( - p.y / L , p.x / L);
 }
 Point GetLineCross(Point p,Vector v,Point q,Vector w){ //交点
     Vector u = p - q;
     double t = Cross(w,u) / Cross(v,w);
     return p + v * t;
 }
 double Distance(Point p,Point a,Point b){  //点到射线的距离
     Vector v1 = b - a;
     Vector v2 = p - a;
     return fabs(Cross(v1,v2)) / Length(v1);
 }
 double Distance2(Point p,Point a,Point b){
     if(a == b)
         return Length(p - a);
     Vector v1 = b - a , v2 = p - a, v3 = p - b;
     if(dcmp(Dot(v1,v2)) < )
         return Length(v2);
     else if(dcmp(Dot(v1,v3)) > )
         return Length(v3);
     else
         return fabs(Cross(v1,v2))/ Length(v1);
 }
 Point GetLinePoint(Point p,Point a,Point b){ //点在线上的投影
     Vector v = b - a;
     return a + v *  (Dot(v, p -a ) / Dot(v,v));
 }
 bool If_Cross(Point a1,Point a2,Point b1,Point b2){  //是否相交
     double c1 = Cross(a2 - a1 , b1 - a1) , c2 = Cross(a2 - a1 , b2 - a1),
            c3 = Cross(b2 - b1,  a1 - b1),  c4  = Cross(b2 - b1, a2 - b1);
     return dcmp(c1) * dcmp(c2) <  && dcmp(c3) * dcmp(c4) < ;
 }
 bool If_InLine(Point p,Point a1,Point a2){
     return dcmp(Cross(a1 - p , a2 - p)) ==  && dcmp(Dot(a1 - p , a2 - p)) < ;
 }