bentleyottmann algorithm

bentleyottmann.cpp

@@ -0,0 +1,54 @@
+#include<bits/stdc++>
+#define x second
+#define y first
+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) {};
+};
+int n,e;
+event events[MAX];
+bool compare(event a, event b) 
+{ 
+    return a.p1.x<b.p1.x; 
+}
+set<point >s;
+void hv_intersection()
+{
+    for (int i=0;i<e;++i)
+        {
+                event c = events[i];
+                if (c.type==0) s.insert(c.p1);//insert starting point of line segment into set
+                else if (c.type==1) s.erase(c.p2);//remove starting point of line segment from set, equivalent to removing line segment
+                else
+                {
+                        for (typeof(s.begin()) it=s.lower_bound(make_pair(c.p1.y,-1));it!=s.end() && it->y<=c.p2.y; it++)
+                                printf("%d, %d\n", events[i].p1.x, it->y);//intersections
+                }
+        }
+}
+int main () 
+{
+    scanf("%d", &n);
+    int p1x,p1y,p2x,p2y;
+        for (int i=0;i<n;++i) 
+        {
+                scanf("%d %d %d %d", &p1x, &p1y,&p2x, &p2y);
+        if(p1x==p2x)               
+        {
+            events[e++]=event(make_pair(p1y,p1x),make_pair(p2y,p2x),2);
+        }
+        else                
+        {
+
+            events[e++]=event(make_pair(p1y,p1x),make_pair(p2y,p2x),0);
+            events[e++]=event(make_pair(p2y,p2x),make_pair(p1y,p1x),1);
+        }
+        }
+    sort(events, events+e,compare);//on x coordinate
+    hv_intersection();
+    return 0;
+}