POJ 1410 Intersection

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
using namespace std;

struct Point
{
double x,y;
};
struct Segment
{
Point p1,p2;
};

double cross(const Point& o,const Point & a,const Point& b)
{
return (a.x - o.x)*(b.y-o.y) - (a.y - o.y)* (b.x - o.x);
}

double dot(const Point& o,const Point & a,const Point& b)
{
return (a.x - o.x) * (b.x - o.x) + (a.y-o.y) * (b.y - o.y);
}

const double eps = 1E-8;
int sig(double d)
{
return (d > eps) - (d < -eps);
}

int btw(const Point& x,const Point& a,const Point&b)
{
return sig(dot(x,a,b));
}

int SegCross(const Point & a,const Point & b,const Point& c,const Point& d)
{
int d1,d2,d3,d4;
d1 = sig(cross(a,b,c));
d2 = sig(cross(a,b,d));
d3 = sig(cross(c,d,a));
d4 = sig(cross(c,d,b));
if((d1^d2)==-2&&(d3^d4)==-2)
{
return 1;

}
if(d1 == 0 && btw(c,a,b)<=0||
d2 == 0 && btw(d,a,b)<=0 ||
d3 == 0 && btw(a,c,d)<=0 ||
d4 == 0 && btw(b,c,d) <=0)
return 2;
return 0;
}

int main()
{
int n;
cin >> n;
Segment seg;
Segment rseg[4];
Point p1,p2,p3,p4;
int flag;
while(n--)
{
flag = 0;
scanf("%lf%lf%lf%lf",&seg.p1.x,&seg.p1.y,&seg.p2.x,&seg.p2.y);
scanf("%lf%lf%lf%lf",&p1.x,&p1.y,&p2.x,&p2.y);
p3.x = p2.x;
p3.y = p1.y;
p4.x = p1.x;
p4.y = p2.y;
flag += SegCross(seg.p1,seg.p2,p1,p3);
flag += SegCross(seg.p1,seg.p2,p1,p4);
flag += SegCross(seg.p1,seg.p2,p2,p3);
flag += SegCross(seg.p1,seg.p2,p2,p4);
//cout << "flag = " << flag << endl;
if(flag)
cout << "T" << endl;
else
{
if((min(p1.x,p2.x) < min(seg.p1.x,seg.p2.x )) &&
(min(p1.y,p2.y) < min(seg.p1.y,seg.p2.y )) &&
(max(p1.x,p2.x) > max(seg.p1.x,seg.p2.x )) &&
(max(p1.y,p2.y) > max(seg.p1.y,seg.p2.y )) )
cout << "T" << endl;
else
cout << "F" << endl;
}

}
return 0;
}