poj 2826

太自闭了。。。明明很水的说。。。

有三种为0的情况。一种是有水平，一种是没交点。

第三种有点难想啊。就是下面那个板子被上面的挡住了，，雨水进不去。。。

关键是我翻了翻discuss找到了这种数据，，但是脑子短路了不知道怎么写。。。

我们只要把下面那个端点向上延长！看和上面的板子有没有交点就行了啊！还是看了kuangbin的代码受到的启发。。。

哇我是傻逼啊。

 #include <cstdio>
 #include <cstring>
 #include <cmath>
 #include <iostream>
 #include <iomanip>

 using namespace std;
 typedef double db;
 const db eps = 1e-;
 const db pi = acos(-);
 int sign(db k){if(k>eps)return ; else if(k<-eps)return -;return ;}
 int cmp(db k1,db k2){ return sign(k1-k2);}
 struct point{
     db x,y;
     point operator+(const point &k1)const { return point{k1.x+x,k1.y+y};}
     point operator - (const point &k1) const{return (point){x-k1.x,y-k1.y};}
     point operator * (db k1) const{return (point){x*k1,y*k1};}
     point operator / (db k1) const{return (point){x/k1,y/k1};}
     db abs(){ return sqrt(x*x+y*y);}
 };
 db cross(point k1,point k2){ return k1.x*k2.y-k1.y*k2.x;}
 db dot(point k1,point k2){ return k1.x*k2.x+k1.y*k2.y;}
 int intersect(db l1,db r1,db l2,db r2){
     if (l1>r1) swap(l1,r1); if (l2>r2) swap(l2,r2); return cmp(r1,l2)!=-&&cmp(r2,l1)!=-;
 }
 int checkSS(point k1,point k2,point k3,point k4){
     return intersect(k1.x,k2.x,k3.x,k4.x)&&intersect(k1.y,k2.y,k3.y,k4.y)&&
            sign(cross(k3-k1,k4-k1))*sign(cross(k3-k2,k4-k2))<=&&
            sign(cross(k1-k3,k2-k3))*sign(cross(k1-k4,k2-k4))<=;
 }
 point getLL(point k1,point k2,point k3,point k4){
     db w1=cross(k1-k3,k4-k3),w2=cross(k4-k3,k2-k3); return (k1*w2+k2*w1)/(w1+w2);
 }
 point p[];
 int t;
 int main(){
     ios::sync_with_stdio(false);
     cout<<fixed<<setprecision();
     cin>>t;
     while (t--) {
         for (int i = ; i <= ; i++) {
             cin >> p[i].x >> p[i].y;
         }
         bool f=;
         if(cmp(p[].y,p[].y)==)f=;
         if(cmp(p[].y,p[].y)==)f=;
         if(!checkSS(p[],p[],p[],p[]))f=;
         if(!f){
             cout<<0.00<<endl;
             continue;
         }
         point tmp = getLL(p[],p[],p[],p[]);
         if(p[].y<p[].y) swap(p[],p[]);
         if(p[].y<p[].y) swap(p[],p[]);
         if(p[].y>p[].y){//maxy=p[1]
             point ano = getLL(p[],tmp,p[],{p[].x-,p[].y});
             if (checkSS({p[].x,p[].y},{p[].x,},ano,p[])){
                 cout<<0.00<<endl;
                 continue;
             }
             db ans = cross(p[]-tmp,ano-tmp)/;
             ans=abs(ans);
             cout<<ans<<endl;
         } else{
             point ano = getLL(p[],tmp,p[],{p[].x-,p[].y});
             if (checkSS({p[].x,p[].y},{p[].x,},ano,p[])){
                 cout<<0.00<<endl;
                 continue;
             }
             db ans = cross(p[]-tmp,ano-tmp)/;
             ans=abs(ans);
             cout<<ans<<endl;
         }
     }
 }
 /**
 1
 0 0 10 10
 0 0 8 9
  */