geometry - C++ : Modified Line Segment Intersection -

given n lines (either horizontal or vertical), need find total intersection of these line segments intersections per line. code follows :

using namespace std;  #define x second #define y first #define max 10000  typedef pair<int,int >point; struct event  {     point p1,p2;     int type;     event() {};     event(point p1,point p2, int type) : p1(p1), p2(p2),type(type) {};  //initialization of event }; int n,e; event events[max]; bool compare(event a, event b)  {      return a.p1.x<b.p1.x;  } set<point >s; int hv_intersection() {     ll count=0;     (ll i=0;i<e;++i)         {                 event c = events[i];                 if (c.type==0) s.insert(c.p1);//insert starting point of line segment set                 else if (c.type==1) s.erase(c.p2);//remove starting point of line segment set, equivalent removing line segment                 else                 {                         (typeof(s.begin()) it=s.lower_bound(make_pair(c.p1.y,-1));it!=s.end() && it->y<=c.p2.y; it++) // range search                             {    printf("%d, %d\n", events[i].p1.x, it->y);//intersections                                 count++;                             }                 }         }      return count; } int main ()  {      scanf("%d", &n);     ll p1x,p1y,p2x,p2y;         (int i=0;i<n;++i)          {                 scanf("%d %d %d %d", &p1x, &p1y,&p2x, &p2y);         if(p1x==p2x)                //if vertical line, 1 event type=2         {             events[e++]=event(make_pair(p1y,p1x),make_pair(p2y,p2x),2);         }         else                    //if horizontal line, 2 events 1 starting point , 1 ending point         {             //store both starting points , ending points             events[e++]=event(make_pair(p1y,p1x),make_pair(p2y,p2x),0);             //store both ending , starting points, note order in second, because sort on p1, ending points first, remove line when hit ending point , need starting point removal of line             events[e++]=event(make_pair(p2y,p2x),make_pair(p1y,p1x),1);         }         }     sort(events, events+e,compare);//on x coordinate    int count= hv_intersection();      cout<<"count="<<count;     return 0; } 

for following input :

5                                   // number of lines 0 0 0 3                             // x1,y1,x2,y2 2 0 2 5  3 0 3 5 0 0 3 0 0 3 3 3 

output :

2, 0 2, 3 3, 0 3, 3 count=4 

now can't figure out how following things :

1.the intersection should not there when both line segments end point meet. 1 end point can lie on other line segment though i.e (3,0) incorrect. valid intersection points according conditions :

(2,0) , (2,3), (3,3) 

2. want calculate number of intersections per line i.e. desired output should be:

0 2 1 1 2  count=3  

i.e.

0 0 0 3   has 0 intersection 2 0 2 5   has 2 intersections 3 0 3 5   has 1 intersection 0 0 3 0   has 1 intersection 0 3 3 3   has 2 intersections 

can me out in correcting these 2 mistakes in code ?