codeforces 13 b

给你三根线段判段是否组成了A

条件，两条线段交于端点并且夹角不大于90，第三条线段端点在两条线段上并且划分的大小满足 大:小<4:1

注释很全。(主要是我记不清楚了，，好像过了一个多星期了)

 #include <bits/stdc++.h>
 using namespace std;
 typedef long long ll;
 typedef long long db;
 int inmid(db k1,db k2,db k3){return (k1-k3)*(k2-k3)<=;}// k3 在 [k1,k2] 内
 struct point{
     ll 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};}
     int operator == (const point &k1) const{return x==k1.x&&y==k1.y;}
 };
 int inmid(point k1,point k2,point k3){return inmid(k1.x,k2.x,k3.x)&&inmid(k1.y,k2.y,k3.y);}
 ll cross(point k1,point k2){return k1.x*k2.y-k1.y*k2.x;}
 ll dot(point k1,point k2){return k1.x*k2.x+k1.y*k2.y;}
 struct line {
     // p[0]->p[1]
     point p[];
     line(point k1, point k2) {p[] = k1;p[] = k2;}
     point &operator[](int k) { return p[k]; }
 };
 ll cross(line a,line b){return cross(a[]-a[],b[]-b[]);}
 ll dot(line a,line b){return dot(a[]-a[],b[]-b[]);}
 int t;point p[];
 vector<line> l;
 bool check(ll x,ll y){if(x*<y)return ;if(x*>y*)return ;return ;}
 bool slove(line a,line b,line c){
     if(a[]==b[])swap(a[],a[]),swap(b[],b[]);
     if(a[]==b[])swap(a[],a[]);
     if(a[]==b[])swap(b[],b[]);
     if(!(a[]==b[]))return ;//判相交
     if(cross(a,b)==)return ;//重合
     if(dot(a,b)<)return ;//夹角
     if(cross(a[]-a[],c[]-a[])==&&cross(b[]-b[],c[]-b[])==){}
     else swap(c[],c[]);
     if(!(cross(a[]-a[],c[]-a[])==&&cross(b[]-b[],c[]-b[])==))return ;//共线
     if(!inmid(a[],a[],c[]))return ;//在线段上
     if(!inmid(b[],b[],c[]))return ;
     //比例
     if(!check(abs(a[].x-c[].x),abs(a[].x-a[].x)))return ;
     if(!check(abs(a[].y-c[].y),abs(a[].y-a[].y)))return ;
     if(!check(abs(b[].x-c[].x),abs(b[].x-b[].x)))return ;
     if(!check(abs(b[].y-c[].y),abs(b[].y-b[].y)))return ;
     return ;
 }
 
 int main(){
     scanf("%d",&t);
     while(t--){
         l.clear();
         for(int i=;i<=;i++)scanf("%lld%lld",&p[i].x,&p[i].y);
         l.push_back({p[],p[]});l.push_back({p[],p[]});l.push_back({p[],p[]});
         if(slove(l[],l[],l[]))cout<<"YES"<<endl;
         else if(slove(l[],l[],l[]))cout<<"YES"<<endl;
         else if(slove(l[],l[],l[]))cout<<"YES"<<endl;
         else cout<<"NO"<<endl;
     }
 }
 /**
 1
 0 0 0 6
 0 6 2 -4
 1 1 0 1
  */