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#include "geometry/convex_hull.hpp"
#include "geometry/robust_orientation.hpp"
#include "base/stl_helpers.hpp"
#include <algorithm>
using namespace std;
namespace m2
{
namespace
{
// Checks whether (p1 - p) x (p2 - p) > 0.
bool IsCCW(PointD const & p1, PointD const & p2, PointD const & p, double eps)
{
return robust::OrientedS(p1, p2, p) > eps;
}
bool IsContinuedBy(vector<PointD> const & hull, PointD const & p, double eps)
{
auto const n = hull.size();
if (n < 2)
return true;
auto const & p1 = hull[n - 2];
auto const & p2 = hull[n - 1];
// Checks whether (p2 - p1) x (p - p2) > 0.
return IsCCW(p, p1, p2, eps);
}
vector<PointD> BuildConvexHull(vector<PointD> points, double eps)
{
base::SortUnique(points);
auto const n = points.size();
if (n < 2)
return points;
iter_swap(points.begin(), min_element(points.begin(), points.end()));
auto const pivot = points[0];
sort(points.begin() + 1, points.end(), [&pivot, &eps](PointD const & lhs, PointD const & rhs) {
if (IsCCW(lhs, rhs, pivot, eps))
return true;
if (IsCCW(rhs, lhs, pivot, eps))
return false;
return lhs.SquaredLength(pivot) < rhs.SquaredLength(pivot);
});
vector<PointD> hull;
for (auto const & p : points)
{
while (!IsContinuedBy(hull, p, eps))
hull.pop_back();
hull.push_back(p);
}
return hull;
}
} // namespace
ConvexHull::ConvexHull(vector<PointD> const & points, double eps)
: m_hull(BuildConvexHull(points, eps))
{
}
} // namespace m2
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