POJ 2826 An Easy Problem?![线段]

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <vector>
using namespace std;
typedef long long ll;
const double eps=1e-8;
inline int read(){
    char c=getchar();int x=0,f=1;
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1; c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘; c=getchar();}
    return x*f;
}
inline int sgn(double x){
    if(abs(x)<eps) return 0;
    else return x<0?-1:1;
}
struct Vector{
    double x,y;
    Vector(double a=0,double b=0):x(a),y(b){}
    bool operator <(const Vector &a)const{
        return x<a.x||(x==a.x&&y<a.y);
    }
    void print(){
        printf("%lf %lf\n",x,y);
    }
};
typedef Vector Point;
Vector operator +(Vector a,Vector b){return Vector(a.x+b.x,a.y+b.y);}
Vector operator -(Vector a,Vector b){return Vector(a.x-b.x,a.y-b.y);}
Vector operator *(Vector a,double b){return Vector(a.x*b,a.y*b);}
Vector operator /(Vector a,double b){return Vector(a.x/b,a.y/b);}
bool operator ==(Vector a,Vector b){return sgn(a.x-b.x)==0&&sgn(a.y-b.y)==0;}

double Cross(Vector a,Vector b){
    return a.x*b.y-a.y*b.x;
}
double Dot(Vector a,Vector b){
    return a.x*b.x+a.y*b.y;
}
double DisPP(Point a,Point b){
    Point t=a-b;
    return sqrt(t.x*t.x+t.y*t.y);
}
double Len(Vector a){return sqrt(Dot(a,a));}
struct Line{
    Point s,t;
    Line(){}
    Line(Point p,Point v):s(p),t(v){}
};

bool isLSI(Line l1,Line l2){
    Vector v=l1.t-l1.s,u=l2.s-l1.s,w=l2.t-l1.s;
    return sgn(Cross(v,u))!=sgn(Cross(v,w));
}
bool isSSI(Line l1,Line l2){
    return isLSI(l1,l2)&&isLSI(l2,l1);
}
Point LI(Line a,Line b){
    Vector v=a.s-b.s,v1=a.t-a.s,v2=b.t-b.s;
    double t=Cross(v2,v)/Cross(v1,v2);
    return a.s+v1*t;
}

double DisTL(Point p,Point a,Point b){
    Vector v1=b-a,v2=p-a;
    return abs(Cross(v1,v2)/Len(v1));
}

int n;
double x,y,x2,y2;
Line l1,l2;
double solve(){
    if(sgn(l1.s.y-l1.t.y)==0||sgn(l2.s.y-l2.t.y)==0) return 0;
    if(sgn(Cross(l1.t-l1.s,l2.t-l2.s))==0) return 0;
    if(!isSSI(l1,l2)) return 0;
    
    if(l1.s.y>l1.t.y) swap(l1.s,l1.t);
    if(l2.s.y>l2.t.y) swap(l2.s,l2.t);
    
    if(isSSI(Line(l1.t,Point(l1.t.x,10000)),l2)) return 0;
    if(isSSI(Line(l2.t,Point(l2.t.x,10000)),l1)) return 0;
    //puts("hi");
    Point p=LI(l1,l2),a=l1.t,b=l2.t;//p.print();
    if(a.y>b.y) swap(a,b),swap(l1,l2);
    
    Line t(a,Point(10000,a.y));
    Point c=LI(t,l2);//c.print();
    return abs(Cross(a-p,c-p))/2;
}
int main(int argc, const char * argv[]) {
    int T=read();
    while(T--){
        scanf("%lf%lf%lf%lf",&x,&y,&x2,&y2);
        l1=Line(Point(x,y),Point(x2,y2));
        scanf("%lf%lf%lf%lf",&x,&y,&x2,&y2);
        l2=Line(Point(x,y),Point(x2,y2));
        printf("%.2f\n",solve()+eps);
    }
    return 0;
}