closest_pair.hpp¶
求平面点集中欧氏距离最近的一对点，并返回原下标；避免枚举所有点对。
Complexity: Time: O(n log n). Space: O(n).
AC 记录：closest_pair。
Implementation¶
当前头文件，省略 include guard；依赖见 #include。
/// @complexity Time: O(n log n).
/// Space: O(n).
#include "noya/geometry_base.hpp"
#include <algorithm>
#include <cassert>
#include <optional>
#include <utility>
#include <vector>
namespace noya {
/// @brief Return indices of a closest pair in O(n log n).
template <class T>
std::pair<int, int> closest_pair(const std::vector<point<T>> &pt) {
assert(pt.size() >= 2);
struct indexed_point {
point<T> val;
int idx;
};
using distance_type = decltype(norm2(point<T>{}));
std::vector<indexed_point> ord;
for (int idx = 0; idx < int(pt.size()); idx++) {
ord.push_back({pt[idx], idx});
}
std::sort(ord.begin(), ord.end(),
[](const indexed_point &a, const indexed_point &b) {
if (a.val != b.val) {
return a.val < b.val;
}
return a.idx < b.idx;
});
for (int i = 1; i < int(ord.size()); i++) {
if (ord[i - 1].val == ord[i].val) {
return std::minmax(ord[i - 1].idx, ord[i].idx);
}
}
std::optional<distance_type> bst;
std::pair<int, int> ans = {-1, -1};
auto upd = [&](const indexed_point &a, const indexed_point &b) {
distance_type can = norm2(a.val - b.val);
if (!bst || can < *bst) {
bst = can;
ans = std::minmax(a.idx, b.idx);
}
};
auto by = [](const indexed_point &a, const indexed_point &b) {
if (a.val.y != b.val.y) {
return a.val.y < b.val.y;
}
if (a.val.x != b.val.x) {
return a.val.x < b.val.x;
}
return a.idx < b.idx;
};
auto dfs = [&](auto &self, int l, int r) -> void {
if (r - l <= 3) {
for (int i = l; i < r; i++) {
for (int j = l; j < i; j++) {
upd(ord[i], ord[j]);
}
}
std::sort(ord.begin() + l, ord.begin() + r, by);
return;
}
int mid = (l + r) / 2;
T xm = ord[mid].val.x;
self(self, l, mid);
self(self, mid, r);
std::inplace_merge(ord.begin() + l, ord.begin() + mid, ord.begin() + r, by);
std::vector<indexed_point> buf;
for (int i = l; i < r; i++) {
distance_type dx = ord[i].val.x - xm;
if (dx * dx > *bst) {
continue;
}
for (int j = int(buf.size()) - 1; j >= 0; j--) {
distance_type dy = ord[i].val.y - buf[j].val.y;
if (dy * dy > *bst) {
break;
}
upd(ord[i], buf[j]);
}
buf.push_back(ord[i]);
}
};
dfs(dfs, 0, int(ord.size()));
return ans;
}
} // namespace noya
#ifndef NOYA_CLOSEST_PAIR_HPP
#define NOYA_CLOSEST_PAIR_HPP 1
/// @complexity Time: O(n log n).
/// Space: O(n).
#include "noya/geometry_base.hpp"
#include <algorithm>
#include <cassert>
#include <optional>
#include <utility>
#include <vector>
namespace noya {
/// @brief Return indices of a closest pair in O(n log n).
template <class T>
std::pair<int, int> closest_pair(const std::vector<point<T>> &pt) {
assert(pt.size() >= 2);
struct indexed_point {
point<T> val;
int idx;
};
using distance_type = decltype(norm2(point<T>{}));
std::vector<indexed_point> ord;
for (int idx = 0; idx < int(pt.size()); idx++) {
ord.push_back({pt[idx], idx});
}
std::sort(ord.begin(), ord.end(),
[](const indexed_point &a, const indexed_point &b) {
if (a.val != b.val) {
return a.val < b.val;
}
return a.idx < b.idx;
});
for (int i = 1; i < int(ord.size()); i++) {
if (ord[i - 1].val == ord[i].val) {
return std::minmax(ord[i - 1].idx, ord[i].idx);
}
}
std::optional<distance_type> bst;
std::pair<int, int> ans = {-1, -1};
auto upd = [&](const indexed_point &a, const indexed_point &b) {
distance_type can = norm2(a.val - b.val);
if (!bst || can < *bst) {
bst = can;
ans = std::minmax(a.idx, b.idx);
}
};
auto by = [](const indexed_point &a, const indexed_point &b) {
if (a.val.y != b.val.y) {
return a.val.y < b.val.y;
}
if (a.val.x != b.val.x) {
return a.val.x < b.val.x;
}
return a.idx < b.idx;
};
auto dfs = [&](auto &self, int l, int r) -> void {
if (r - l <= 3) {
for (int i = l; i < r; i++) {
for (int j = l; j < i; j++) {
upd(ord[i], ord[j]);
}
}
std::sort(ord.begin() + l, ord.begin() + r, by);
return;
}
int mid = (l + r) / 2;
T xm = ord[mid].val.x;
self(self, l, mid);
self(self, mid, r);
std::inplace_merge(ord.begin() + l, ord.begin() + mid, ord.begin() + r, by);
std::vector<indexed_point> buf;
for (int i = l; i < r; i++) {
distance_type dx = ord[i].val.x - xm;
if (dx * dx > *bst) {
continue;
}
for (int j = int(buf.size()) - 1; j >= 0; j--) {
distance_type dy = ord[i].val.y - buf[j].val.y;
if (dy * dy > *bst) {
break;
}
upd(ord[i], buf[j]);
}
buf.push_back(ord[i]);
}
};
dfs(dfs, 0, int(ord.size()));
return ans;
}
} // namespace noya
#endif // NOYA_CLOSEST_PAIR_HPP
#include <algorithm>
#include <cassert>
#include <cmath>
#include <optional>
#include <utility>
#include <vector>
/// @complexity Time: O(n log n).
/// Space: O(n).
/// @complexity Time: O(1) per primitive; O(n log n) for convex hull.
/// Space: O(1) per primitive and O(n) for hull construction.
namespace noya {
/// @brief Two-dimensional point with vector arithmetic and lexicographic order.
template <class T> struct point {
T x{};
T y{};
point() = default;
point(T x_, T y_) : x(x_), y(y_) {}
point &operator+=(const point &rhs) {
x += rhs.x;
y += rhs.y;
return *this;
}
point &operator-=(const point &rhs) {
x -= rhs.x;
y -= rhs.y;
return *this;
}
point &operator*=(const T &scl) {
x *= scl;
y *= scl;
return *this;
}
point &operator/=(const T &scl) {
x /= scl;
y /= scl;
return *this;
}
friend point operator+(point l, const point &r) { return l += r; }
friend point operator-(point l, const point &r) { return l -= r; }
friend point operator*(point val, const T &scl) { return val *= scl; }
friend point operator*(const T &scl, point val) { return val *= scl; }
friend point operator/(point val, const T &scl) { return val /= scl; }
friend bool operator==(const point &, const point &) = default;
friend bool operator<(const point &l, const point &r) {
return l.x < r.x || (l.x == r.x && l.y < r.y);
}
};
/// @brief Circle represented by a center and a nonnegative radius.
template <class Real> struct circle {
point<Real> o;
Real r1{};
};
/// @brief Return the dot product of two vectors.
template <class T> T dot(const point<T> &a, const point<T> &b) {
return a.x * b.x + a.y * b.y;
}
/// @brief Return the signed cross product of two vectors.
template <class T> T cross(const point<T> &a, const point<T> &b) {
return a.x * b.y - a.y * b.x;
}
/// @brief Return cross(a - o1, b - o1).
template <class T>
T cross(const point<T> &o1, const point<T> &a, const point<T> &b) {
return cross(a - o1, b - o1);
}
/// @brief Return the squared Euclidean norm.
template <class T> T norm2(const point<T> &val) { return dot(val, val); }
/// @brief Compare a value with zero using an optional absolute tolerance.
template <class T> int sign(const T &val, const T &eps = T{}) {
return (val > eps) - (val < -eps);
}
/// @brief Return -1, 0, or 1 for a clockwise, collinear, or counter-clockwise
/// turn.
template <class T>
int orientation(const point<T> &a, const point<T> &b, const point<T> &c,
const T &eps = T{}) {
return sign(cross(a, b, c), eps);
}
/// @brief Test whether p lies on the closed segment [a, b].
template <class T>
bool on_segment(const point<T> &p, const point<T> &a, const point<T> &b,
const T &eps = T{}) {
if (orientation(a, b, p, eps) != 0) {
return false;
}
return std::min(a.x, b.x) - eps <= p.x && p.x <= std::max(a.x, b.x) + eps &&
std::min(a.y, b.y) - eps <= p.y && p.y <= std::max(a.y, b.y) + eps;
}
/// @brief Test whether the closed segments [a, b] and [c, d] intersect.
template <class T>
bool segments_intersect(const point<T> &a, const point<T> &b, const point<T> &c,
const point<T> &d, const T &eps = T{}) {
int s1 = orientation(a, b, c, eps);
int s2 = orientation(a, b, d, eps);
int s3 = orientation(c, d, a, eps);
int s4 = orientation(c, d, b, eps);
if (s1 == 0 && on_segment(c, a, b, eps)) {
return true;
}
if (s2 == 0 && on_segment(d, a, b, eps)) {
return true;
}
if (s3 == 0 && on_segment(a, c, d, eps)) {
return true;
}
if (s4 == 0 && on_segment(b, c, d, eps)) {
return true;
}
return s1 * s2 < 0 && s3 * s4 < 0;
}
/// @brief Intersect the infinite lines through (a, b) and (c, d), returning
/// nullopt when they are parallel or coincident.
template <class T>
std::optional<point<long double>>
line_intersection(const point<T> &a, const point<T> &b, const point<T> &c,
const point<T> &d, long double eps = 0) {
point<long double> lhs{static_cast<long double>(a.x),
static_cast<long double>(a.y)};
point<long double> b1{static_cast<long double>(b.x),
static_cast<long double>(b.y)};
point<long double> z{static_cast<long double>(c.x),
static_cast<long double>(c.y)};
point<long double> d1{static_cast<long double>(d.x),
static_cast<long double>(d.y)};
point<long double> da = b1 - lhs;
point<long double> db = d1 - z;
long double den = cross(da, db);
if (std::abs(den) <= eps) {
return std::nullopt;
}
long double rat = cross(z - lhs, db) / den;
return lhs + da * rat;
}
/// @brief Return the convex hull in counter-clockwise order without repetition.
template <class T>
std::vector<point<T>> convex_hull(std::vector<point<T>> pt, bool kc = false) {
std::sort(pt.begin(), pt.end());
pt.erase(std::unique(pt.begin(), pt.end()), pt.end());
if (pt.size() <= 1) {
return pt;
}
bool col = true;
for (int i = 2; i < int(pt.size()); i++) {
col &= orientation(pt[0], pt[1], pt[i]) == 0;
}
if (kc && col) {
return pt;
}
std::vector<point<T>> lo, hi;
for (const point<T> &p : pt) {
while (lo.size() >= 2) {
int rot = orientation(lo[lo.size() - 2], lo.back(), p);
if (rot > 0 || (kc && rot == 0)) {
break;
}
lo.pop_back();
}
lo.push_back(p);
}
for (auto it = pt.rbegin(); it != pt.rend(); ++it) {
while (hi.size() >= 2) {
int rot = orientation(hi[hi.size() - 2], hi.back(), *it);
if (rot > 0 || (kc && rot == 0)) {
break;
}
hi.pop_back();
}
hi.push_back(*it);
}
lo.pop_back();
hi.pop_back();
lo.insert(lo.end(), hi.begin(), hi.end());
return lo;
}
/// @brief Return twice the signed area of a polygon.
template <class T> T polygon_area2(const std::vector<point<T>> &pg) {
T res{};
for (int i = 0; i < int(pg.size()); i++) {
res += cross(pg[i], pg[(i + 1) % pg.size()]);
}
return res;
}
/// @brief Classify a point relative to a polygon: -1 outside, 0 boundary, 1
/// inside.
template <class T>
int point_in_polygon(const point<T> &p, const std::vector<point<T>> &pg) {
bool in = false;
for (int i = 0; i < int(pg.size()); i++) {
point<T> a = pg[i];
point<T> b = pg[(i + 1) % pg.size()];
if (on_segment(p, a, b)) {
return 0;
}
if (a.y <= p.y && p.y < b.y && orientation(a, b, p) > 0) {
in = !in;
}
if (b.y <= p.y && p.y < a.y && orientation(a, b, p) < 0) {
in = !in;
}
}
return in ? 1 : -1;
}
/// @brief Return the Euclidean distance between two points.
template <class T> long double distance(const point<T> &a, const point<T> &b) {
return std::hypot(
static_cast<long double>(a.x) - static_cast<long double>(b.x),
static_cast<long double>(a.y) - static_cast<long double>(b.y));
}
} // namespace noya
namespace noya {
/// @brief Return indices of a closest pair in O(n log n).
template <class T>
std::pair<int, int> closest_pair(const std::vector<point<T>> &pt) {
assert(pt.size() >= 2);
struct indexed_point {
point<T> val;
int idx;
};
using distance_type = decltype(norm2(point<T>{}));
std::vector<indexed_point> ord;
for (int idx = 0; idx < int(pt.size()); idx++) {
ord.push_back({pt[idx], idx});
}
std::sort(ord.begin(), ord.end(),
[](const indexed_point &a, const indexed_point &b) {
if (a.val != b.val) {
return a.val < b.val;
}
return a.idx < b.idx;
});
for (int i = 1; i < int(ord.size()); i++) {
if (ord[i - 1].val == ord[i].val) {
return std::minmax(ord[i - 1].idx, ord[i].idx);
}
}
std::optional<distance_type> bst;
std::pair<int, int> ans = {-1, -1};
auto upd = [&](const indexed_point &a, const indexed_point &b) {
distance_type can = norm2(a.val - b.val);
if (!bst || can < *bst) {
bst = can;
ans = std::minmax(a.idx, b.idx);
}
};
auto by = [](const indexed_point &a, const indexed_point &b) {
if (a.val.y != b.val.y) {
return a.val.y < b.val.y;
}
if (a.val.x != b.val.x) {
return a.val.x < b.val.x;
}
return a.idx < b.idx;
};
auto dfs = [&](auto &self, int l, int r) -> void {
if (r - l <= 3) {
for (int i = l; i < r; i++) {
for (int j = l; j < i; j++) {
upd(ord[i], ord[j]);
}
}
std::sort(ord.begin() + l, ord.begin() + r, by);
return;
}
int mid = (l + r) / 2;
T xm = ord[mid].val.x;
self(self, l, mid);
self(self, mid, r);
std::inplace_merge(ord.begin() + l, ord.begin() + mid, ord.begin() + r, by);
std::vector<indexed_point> buf;
for (int i = l; i < r; i++) {
distance_type dx = ord[i].val.x - xm;
if (dx * dx > *bst) {
continue;
}
for (int j = int(buf.size()) - 1; j >= 0; j--) {
distance_type dy = ord[i].val.y - buf[j].val.y;
if (dy * dy > *bst) {
break;
}
upd(ord[i], buf[j]);
}
buf.push_back(ord[i]);
}
};
dfs(dfs, 0, int(ord.size()));
return ans;
}
} // namespace noya