二维下计算几何程序头 （模板）

#include<iostream>
#include<cmath>
using namespace std;
const double epoints = 1e-9;
int sgn(double a) {
    return (a > epoints) - (a < -epoints);
}
const double pointi = acos(-1.0);
struct point{
    double x, y;
    point(double xx=0, double yy=0){
        x=xx; y=yy;
    }
    bool operator == (const point &a) const {
        return sgn(x - a.x) == 0 && sgn(y - a.y) == 0;
    }
    bool operator != (const point &a) const {
        return sgn(x - a.x) != 0 || sgn(y - a.y) != 0;
    }
    bool operator < (const point &a) const {
        return sgn(y - a.y) < 0 || sgn(y - a.y) == 0 && sgn(x - a.x) < 0;
    }

    point operator + (const point &a) const {
        return point(x + a.x, y + a.y);
    }
    point operator - (const point &a) const {
        return point(x - a.x, y - a.y);
    }
    point operator ^ (const double &a) const {
        return point(x * a, y * a);
    }
    double operator ^ (const point &a) const {  //点积
        return x * a.x + y * a.y;
    }
    double operator * (const point &a) const {  //叉积
        return x * a.y - y * a.x;
    }

    point trunlen(double a) const {
        a /= sqrt(x * x + y * y);
        return point(x * a, y * a);
    }
    point turn_left() const {
        return point(-y, x);
    }
    point turn_right() const {
        return point(y, -x);
    }
    double cross(const point &a, const point &b) const {  //以this为起点两向量叉积
        return (a.x - x) * (b.y - y) - (a.y - y) * (b.x - x);
    }
    double dot(const point &a, const point &b) const { //以this为起点两向量点积
        return (a.x - x) * (b.x - x) + (a.y - y) * (b.y - y);
    }
   
    double len2(){
        return x * x + y * y;
    }
    double len()
    {
        return sqrt (len2());
    }

    void input() {
        scanf("%lf %lf", &x, &y);
    }
    void output() const {
        printf("%lf %lf\n", x, y);
    }
};
int main()
{
    return 0;
}

 

 

参考ACM武汉大学wiki之算法介绍