线段交模板

http://icpc.upc.edu.cn/problem.php?cid=1762&pid=2

#include<bits/stdc++.h>
using namespace std;
struct node{
    double x;
    double y;
};
struct Line{
    node s,e;
};
Line l[110];
bool judge(node a,node b,node c,node d)
{
    if(min(a.x,b.x) <= max(c.x,d.x) && min(c.x,d.x) <= max(a.x,b.x) && min(a.y,b.y) <= max(c.y,d.y) &&min(c.y,d.y)<=max(a.y,b.y))
    {

        double u,v,w,z;
        u=(c.x-a.x)*(b.y-a.y)-(b.x-a.x)*(c.y-a.y);
        v=(d.x-a.x)*(b.y-a.y)-(b.x-a.x)*(d.y-a.y);
        w=(a.x-c.x)*(d.y-c.y)-(d.x-c.x)*(a.y-c.y);
        z=(b.x-c.x)*(d.y-c.y)-(d.x-c.x)*(b.y-c.y);

        return (u*v<=0.00000001 && w*z<=0.00000001);
    }
    return false;
}
int n;
int main()
{
    scanf("%d",&n);
    int ans=0;
    for(int i=1;i<=n;i++)
    {
        scanf("%lf%lf%lf%lf",&l[i].s.x,&l[i].s.y,&l[i].e.x,&l[i].e.y);
        for(int j=1;j<i;j++)
        {
            ans+=judge(l[j].s,l[j].e,l[i].s,l[i].e);
        }
    }
    cout<<ans<<endl;
    return 0;
}