poj3304Segments（直线与多条线段相交）

链接

枚举两点（端点），循环遍历与直线相交的线段。

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 105
 #define LL long long
 #define INF 0xfffffff
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 struct point
 {
     double x,y;
     point(double x=,double y = ):x(x),y(y){}
 }p[N<<];
 struct line
 {
     point a,b;
 };
 typedef point pointt ;
 pointt operator -(point a,point b)
 {
     return point(a.x-b.x,a.y-b.y);
 }
 int dcmp(double x)
 {
     if(fabs(x)<eps) return ;
     return x<?-:;
 }
 double cross(point a,point b)
 {
     return a.x*b.y-a.y*b.x;
 }
 double xmult(point a,point b,point c)
 {
     return cross(a-c,b-c);
 }
 int dotline(point p,line l)
 {
     return (!dcmp(xmult(p,l.a,l.b)))&&(l.a.x-p.x)*(l.b.x-p.x)<eps
                 &&(l.a.y-p.y)*(l.b.y-p.y)<eps;
 }
 double dis(point a)
 {
     return sqrt(a.x*a.x+a.y*a.y);
 }
 int Intersection( point a,point b,point c,point d )
 {
     int d1,d2;
     d1 = dcmp(xmult( a,c,b ));
     d2 = dcmp(xmult( a,d,b ));
     if( d1*d2==- ) return ;//规范相交
      if( d1==||d2== ) return ;//非规范相交
     return ;//不相交
 }
 int main()
 {
     int t,i,j,n,g;
     cin>>t;
     while(t--)
     {
         cin>>n;
         for(i=  ; i <= n; i++)
         {
             scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&p[i+n].x,&p[i+n].y);
         }
         if(n==||n==)
         {
             puts("Yes!");
             continue;
         }
         int flag = ;
         for(i = ; i <= *n;  i++)
         {
             for(j = i+; j<= *n; j++)
             {
                 line l1;
                 l1.a = p[i],l1.b = p[j];
                 if(dcmp(dis(p[i]-p[j]))==) continue;
                 int num = ;
                 for(g = ; g <= n ;g++)
                 {
                    if(Intersection(p[i],p[j],p[g],p[g+n])) num++;
                    else break;
                 }
                 if(num==n)
                 {
                     flag = ;
                     break;
                 }
             }
             if(flag) break;
         }
         if(flag) puts("Yes!");
         else puts("No!");
     }
     return ;
 }