51nod 1264 线段相交（计算几何）

#include <iostream>#include <cstdio>#include <algorithm>#include <cmath>using namespace std;/*计算几何输入两条线段的四个端点，判断两直线是否相交*/const double esp=1e-7;int sgn(double x){    if(fabs(x)<esp) return 0;    if(x<0) return -1;    else return 1;}struct Point{    double x,y;    Point() {}    Point(double _x,double _y)    {        x=_x;        y=_y;    }    Point operator -(const Point &b) const    {        return Point(x-b.x,y-b.y);    }    double operator ^ (const Point &b) const//叉积    {        return x*b.y-y*b.x;    }     double operator * (const Point &b) const//点积    {        return x*b.x+y*b.y;    }    double distance(Point p)//两点距离    {        return hypot(x-p.x,y-p.y);        //return (x-p.x)*(x-p.x)+(y-p.y)*(y-p.y);    }};struct Line{    Point s,e;    Line(){}    Line(Point _s,Point _e)    {        s=_s;        e=_e;    }    double length()//线段长度    {        return s.distance(e);    }    double dispointtoline(Point p)//点到直线距离    {        return fabs((p-s)^(e-s))/length();    }    double dispointtoseg(Point p)//点到线段距离    {        if(sgn((p-s)*(e-s))<0||sgn((p-e)*(s-e))<0)            return min(p.distance(s),p.distance(e));        return dispointtoline(p);    }    //两线段相交判断    //2 规范相交 1 非规范相交 0 不相交    int segcrossseg(Line v)    {        int d1=sgn((e-s)^(v.s-s));        int d2=sgn((e-s)^(v.e-s));        int d3=sgn((v.e-v.s)^(s-v.s));        int d4=sgn((v.e-v.s)^(e-v.s));        if((d1^d2)==-2&&(d3^d4)==-2) return 2;        return (d1==0&&sgn((v.s-s)*(v.s-e))<=0)        ||(d2==0&&sgn((v.e-s)*(v.e-e))<=0)        ||(d3==0&&sgn((s-v.s)*(s-v.e))<=0)        ||(d4==0&&sgn((e-v.s)*(e-v.e))<=0);    }};int main(){    int t;    scanf("%d",&t);    while(t--)    {       Point point[4];       for(int i=0;i<4;i++)       {           scanf("%lf%lf",&point[i].x,&point[i].y);       }       Line line[2];       line[0]=Line(point[0],point[1]);       line[1]=Line(point[2],point[3]);       int flag=line[0].segcrossseg(line[1]);       if(flag)       {           printf("Yes\n");       }       else       {           printf("No\n");       }    }    return 0;}