POJ 1410 Intersection <计算几何（线段相交判断）>

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

struct Point;
typedef Point Vec;
const double EPS=1e-8;

int dblcmp(double x){
return fabs(x)<EPS?0:(x>0?1:-1);
}

struct Point{
double x,y;
Point(){}
Point(double xx,double yy):x(xx),y(yy){}
Vec operator -(Point p){
return Vec(x-p.x,y-p.y);
}
double operator ^(Vec v){
return x*v.y-y*v.x;
}
};

struct Segment{
Point p1,p2;
Segment(){}
Segment(Point pp1,Point pp2):p1(pp1),p2(pp2){}
bool isCross(Segment s){
return max(p1.x,p2.x)>=min(s.p1.x,s.p2.x)&&
max(s.p1.x,s.p2.x)>=min(p1.x,p2.x)&&
max(p1.y,p2.y)>=min(s.p1.y,s.p2.y)&&
max(s.p1.y,s.p2.y)>=min(p1.y,p2.y)&&
dblcmp((p2-p1)^(s.p1-p1))*dblcmp((p2-p1)^(s.p2-p1))<=0&&
dblcmp((s.p2-s.p1)^(p1-s.p1))*dblcmp((s.p2-s.p1)^(p2-s.p1))<=0;
}
};

struct Rectangle{
Segment s[4];
double area;
Rectangle(){}
Rectangle(double _xLeft,double _yTop,double _xRight,double _yBottom){
double xLeft=min(_xLeft,_xRight);
double xRight=max(_xLeft,_xRight);
double yBottom=min(_yBottom,_yTop);
double yTop=max(_yBottom,_yTop);
s[0]=Segment(Point(xLeft,yBottom),Point(xRight,yBottom));
s[1]=Segment(Point(xRight,yBottom),Point(xRight,yTop));
s[2]=Segment(Point(xRight,yTop),Point(xLeft,yTop));
s[3]=Segment(Point(xLeft,yTop),Point(xLeft,yBottom));
area=(xRight-xLeft)*(yTop-yBottom);
}
bool inRectangle(Point p){
double areaTemp=0.0;
for(int i=0;i<4;++i){
areaTemp+=fabs((s[i].p1-p)^(s[i].p2-p));
}
return fabs(areaTemp/2.0-area)<EPS;
}
bool intersection(Segment seg){
for(int i=0;i<4;++i){
if(seg.isCross(s[i])) return true;
}
return inRectangle(seg.p1);
}
};

int main(){
ios::sync_with_stdio(false);
int n;
cin>>n;
double x1,y1,x2,y2,xl,xr,yt,yb;
while(n--){
cin>>x1>>y1>>x2>>y2>>xl>>yt>>xr>>yb;
if(Rectangle(xl,yt,xr,yb).intersection(Segment(Point(x1,y1),Point(x2,y2))))
cout<<'T'<<endl;
else cout<<'F'<<endl;
}
return 0;
}