Artifact 959cda21c7e42a70dc6791077e124c0aebde0573

• File _lib/geo/area.cpp
  • 2011-02-23 09:21:16 - part of checkin [4fd800b3a8] on branch trunk - Copied from private svn repository. (user: kinaba) [annotate]
• File lib/geo/area.cpp
  • 2011-02-23 11:18:09 - part of checkin [23dfcca431] on branch trunk - renamed _lib to lib (user: kinaba) [annotate]

//-------------------------------------------------------------
// Area of a polygon
//   O(N)
//
// Verified by
//   - SRM 337 Div1 LV3
//   - SRM 486 Div1 LV3
//-------------------------------------------------------------

double outer_prod( pt a, pt b )
{
	return (a.real()*b.imag() - b.real()*a.imag())/2;
}

double area( const vector<pt>& q )
{
	double a = 0.0;

	pt o = q[0];
	for(int i=1; i+1<q.size(); ++i)
		a += outer_prod(q[i]-o, q[i+1]-o);
	return abs(a) / 2;
}