#ifndef __geom_h
#define __geom_h

#include <vector>

using namespace std; 


typedef struct _point2d {
  int x,y; 
} point2D;



/* returns 2 times the signed area of triangle abc. The area is positive if c
   is to the left of ab, and negative if c is to the right of ab
 */
int signed_area2D(point2D a, point2D b, point2D c); 


/* return 1 if p,q,r collinear, and 0 otherwise */
int collinear(point2D p, point2D q, point2D r);


/* return 1 if c is  strictly left of ab; 0 otherwise */
int left (point2D a, point2D b, point2D c); 


/* compute the convex hull of the points in p; the points on the CH
   are returned as a list or vector 
*/
vector<point2D> graham_scan(vector<point2D>);




#endif