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#include "geometry/convex_hull.hpp"
#include "base.hpp"
#include "point.hpp"
#include "polygon.hpp"
namespace geometry {
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_4_A
Polygon convex_hull(Polygon &p, bool strict = true) {
int n = (int)p.size(), k = 0;
if (n <= 2) return p;
sort(begin(p), end(p), compare_x);
vector<Point> ch(2 * n);
auto check = [&](int i) {
return sign(cross(ch[k - 1] - ch[k - 2], p[i] - ch[k - 1])) <= -1 + strict;
};
for (int i = 0; i < n; ch[k++] = p[i++]) {
while (k >= 2 && check(i)) --k;
}
for (int i = n - 2, t = k + 1; i >= 0; ch[k++] = p[i--]) {
while (k >= t && check(i)) --k;
}
ch.resize(k - 1);
return ch;
}
} // namespace geometry
#line 2 "geometry/base.hpp"
namespace geometry {
using Real = double;
const Real EPS = 1e-8;
const Real PI = acos(static_cast<Real>(-1));
enum { OUT, ON, IN };
inline int sign(const Real &r) { return r <= -EPS ? -1 : r >= EPS ? 1 : 0; }
inline bool equals(const Real &a, const Real &b) { return sign(a - b) == 0; }
} // namespace geometry
#line 3 "geometry/point.hpp"
namespace geometry {
using Point = complex<Real>;
istream &operator>>(istream &is, Point &p) {
Real a, b;
is >> a >> b;
p = Point(a, b);
return is;
}
ostream &operator<<(ostream &os, const Point &p) {
return os << real(p) << " " << imag(p);
}
Point operator*(const Point &p, const Real &d) {
return Point(real(p) * d, imag(p) * d);
}
// rotate point p counterclockwise by theta rad
Point rotate(Real theta, const Point &p) {
return Point(cos(theta) * real(p) - sin(theta) * imag(p),
sin(theta) * real(p) + cos(theta) * imag(p));
}
Real cross(const Point &a, const Point &b) {
return real(a) * imag(b) - imag(a) * real(b);
}
Real dot(const Point &a, const Point &b) {
return real(a) * real(b) + imag(a) * imag(b);
}
bool compare_x(const Point &a, const Point &b) {
return equals(real(a), real(b)) ? imag(a) < imag(b) : real(a) < real(b);
}
bool compare_y(const Point &a, const Point &b) {
return equals(imag(a), imag(b)) ? real(a) < real(b) : imag(a) < imag(b);
}
using Points = vector<Point>;
} // namespace geometry
#line 2 "geometry/polygon.hpp"
#line 4 "geometry/polygon.hpp"
namespace geometry {
using Polygon = vector<Point>;
using Polygons = vector<Polygon>;
} // namespace geometry
#line 4 "geometry/convex_hull.hpp"
namespace geometry {
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_4_A
Polygon convex_hull(Polygon &p, bool strict = true) {
int n = (int)p.size(), k = 0;
if (n <= 2) return p;
sort(begin(p), end(p), compare_x);
vector<Point> ch(2 * n);
auto check = [&](int i) {
return sign(cross(ch[k - 1] - ch[k - 2], p[i] - ch[k - 1])) <= -1 + strict;
};
for (int i = 0; i < n; ch[k++] = p[i++]) {
while (k >= 2 && check(i)) --k;
}
for (int i = n - 2, t = k + 1; i >= 0; ch[k++] = p[i--]) {
while (k >= t && check(i)) --k;
}
ch.resize(k - 1);
return ch;
}
} // namespace geometry