POJ 3304 Segments 判断直线和线段相交

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;
#define inf (0x3f3f3f3f)
typedef long long int LL;

#include <iostream>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <string>

const int maxn = 5000+20;
struct coor
{
    double x,y;
    coor(){}
    coor(double xx,double yy):x(xx),y(yy){}
    double operator ^(coor rhs) const //计算叉积（向量积）
    {
        return x*rhs.y - y*rhs.x;
    }
    coor operator -(coor rhs) const //坐标相减，a-b得到向量ba
    {
        return coor(x-rhs.x,y-rhs.y);
    }
    double operator *(coor rhs) const //数量积
    {
        return x*rhs.x + y*rhs.y;
    }
};
const double eps = 1e-8;
struct Line
{
    coor point1,point2;
    Line(){}
    Line(coor xx,coor yy):point1(xx),point2(yy){}
    bool operator &(Line rhs) const //判断直线和rhs线段是否相交
    {
        //自己表示一条直线，然而rhs表示的是线段
        //思路，判断rhs线段上两个端点是否在this直线的同一侧即可，用一侧，就不相交
        coor ff1 = point2 - point1; //直线的方向向量
        return ( ((rhs.point1-point1)^ff1) * ((rhs.point2-point1)^ff1) ) <= 0;//符号不同或者有0，证明相交
    }
}a[maxn];
int n;

bool same (double a,double b)
{
    return fabs(a-b)<eps;
}
bool check (coor aa,coor bb)
{
    Line t = Line(aa,bb);
    for (int i=1;i<=n;++i)
    {
        if (!(t&a[i]))
        {
            return false;
        }
    }
    return true;
}
void work ()
{
    scanf("%d",&n);
    for (int i=1;i<=n;++i)
    {
        scanf("%lf%lf%lf%lf",&a[i].point1.x,&a[i].point1.y,&a[i].point2.x,&a[i].point2.y);
    }
    if (n==1)
    {
        printf ("Yes!\n");
        return ;
    }
    for (int i=1;i<=n;++i)
    {
        for (int j=i+1;j<=n;++j)
        {
            if (check(a[i].point1,a[j].point1))
            {
                printf ("Yes!\n");
                return ;
            }
            if (check(a[i].point1,a[j].point2))
            {
                printf ("Yes!\n");
                return ;
            }
            if (check(a[i].point2,a[j].point1))
            {
                printf ("Yes!\n");
                return ;
            }
            if (check(a[i].point2,a[j].point2))
            {
                printf ("Yes!\n");
                return ;
            }
        }
    }
    printf ("No!\n");
    return ;
}

int main()
{
#ifdef local
    freopen("data.txt","r",stdin);
#endif
    int t;
    scanf("%d",&t);
    while(t--) work();
    return 0;
}