计算几何 || 二维基础模板

</pre><pre name="code" class="cpp">/*几何模版*/
#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;

struct point
{
    double x,y,d;
    point(double a,double b):x(a),y(b){}
    point(){}
};
typedef point vec;
//向量+向量=向量
//点  +向量=点
vec operator +  ( vec a,   vec b)      {  return vec(a.x+b.x,a.y+b.y);}

vec operator -  ( point a, point b)    {  return vec(a.x-b.x,a.y-b.y);}

vec operator *  ( vec a,   double p)   {  return vec(a.x*p,a.y*p);}

vec operator /  ( vec a,   double p)   {  return vec(a.x/p,a.y/p);}

bool operator < ( const point &a,const point &b)
{
     return a.x<b.x || (a.x == b.x &&a.y<b.y);
}

const double eps =1e-6;
int dcmp( double x)
{
    if( fabs(x)<eps )return 0;

    return x < 0?-1:1;
}

bool operator == ( const point &a,const point &b)
{
    return dcmp(a.x-b.x) == 0 && dcmp(a.y-b.y)==0;
}
// 点积（向量 a，向量 b）
double dot( vec a,vec b)    {   return a.x*b.x + a.y*b.y;}

double length( vec a)       {   return sqrt(dot(a,a) );}

//向量 a，b 的夹角
double angle(vec a,vec b)
{
    return acos(    dot(a,b)/length(a)/length(b)    );
}

double cross( vec a,vec b ){    return a.x*b.y - a.y*b.x;}

double area( point a,point b,point c){  return cross(b-a,c-a)/2.0;}

// 向量 a 旋转 rad 弧度
vec rotat(vec a,double rad)
{
    return vec( a.x*cos(rad)-a.y*sin(rad),a.x*sin(rad)+a.y*cos(rad));
}

//两条直线 p+tv 和 q + tw 有唯一交点，当且仅当 cross（v,w）！=0
point getlinetnersection(point p,vec v,point q,vec w)
{
    vec u = p-q;
    double t = cross(w,u) /cross(v,w);
    return p + v*t;
}
//点到直线的距离
double distancetoline( point p,point a,point b)
{
    vec v1 = b-a;
    vec v2 = p-a;
    return fabs( cross(v1,v2) / length(v1));//去绝对值得到有向距离

}
//点到线段的距离
double distosegment( point p,point a,point b)
{
    if( a==b )
        return length(p-a);
    vec v1 = b-a;
    vec v2 = p-a;
    vec v3 = p-b;
    if( dcmp( dot(v1,v2)) < 0 )return length(v2);
    else
        if( dcmp ( dot(v1,v3)) >0 )return length(v3);
    else
        return  fabs( cross(v1,v2)/length(v1) );

}

// 两条线段规范相交：每条线段的两个端点在另一条线段的两侧
bool segproperinter( point a1,point a2,point b1,point b2)
{
     double c1 = cross( a2-a1,  b1-a1 ),
            c2 = cross( a2-a1,  b2-a2 ),
            c3 = cross( b2-b1,  a1-b1 ),
            c4 = cross( b2-b1,  a2-b1 );

    return dcmp( c1 ) * dcmp( c2 ) < 0
            && dcmp( c3 )*dcmp( c4 )<0;
}
//一个点在另外一条线段上(=包括端点
bool onsegment( point p,point a1,point a2)
{
    return dcmp( cross(a1-p,a2-p)) == 0
            && dcmp( dot(a1-p,a2-p))<=0;
}

//多边形面积
double polyarea(point *p,int n)
{
    double area = 0;
    for( int i = 1;i < n-1;++i)
        area += cross( p[i]-p[0],p[i+1]-p[0]);
    return area/2.0;
}

int main()
{
    return 0;
}