Adding some more judges, here and there.

[and.git] / lib / Mi manual de algoritmos / version_world_finals_2009 / src / geometria / polygon_area.cpp

//P es un polígono ordenado anticlockwise.
//Si es clockwise, retorna el area negativa.
//Si no esta ordenado retorna pura mierda.
//P[0] != P[n-1]
double PolygonArea(const vector<point> &p){
  double r = 0.0;
  for (int i=0; i<p.size(); ++i){
    int j = (i+1) % p.size();
    r += p[i].x*p[j].y - p[j].x*p[i].y;
  }
  return r/2.0;
}