87 lines
2.2 KiB
Java
87 lines
2.2 KiB
Java
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import java.util.*;
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public class Closest2Points {
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public static class Point {
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long x, y;
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public Point(long x, long y) {
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this.x = x;
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this.y = y;
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}
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}
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public static final Comparator<Point> CMP_X = (a, b) -> Long.compare(a.x, b.x) != 0 ? Long.compare(a.x, b.x) : Long.compare(a.y, b.y);
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public static final Comparator<Point> CMP_Y = (a, b) -> Long.compare(a.y, b.y);
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public static Point[] findClosestPair(Point[] points) {
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Point[] result = new Point[2];
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Arrays.sort(points, CMP_X);
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rec(points, 0, points.length - 1, result, Long.MAX_VALUE);
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return result;
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}
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static long rec(Point[] points, int l, int r, Point[] result, long mindist) {
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if (l == r)
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return Long.MAX_VALUE;
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int mid = (l + r) >> 1;
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long midx = points[mid].x;
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long d1 = rec(points, l, mid, result, mindist);
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mindist = Math.min(mindist, d1);
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long d2 = rec(points, mid + 1, r, result, mindist);
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mindist = Math.min(mindist, d2);
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Arrays.sort(points, l, r + 1, CMP_Y);
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int[] t = new int[r - l + 1];
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int size = 0;
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for (int i = l; i <= r; i++)
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if (Math.abs(points[i].x - midx) < mindist)
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t[size++] = i;
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for (int i = 0; i < size; i++) {
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for (int j = i + 1; j < size; j++) {
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Point a = points[t[i]];
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Point b = points[t[j]];
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if (b.y - a.y >= mindist)
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break;
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long dist = dist(a, b);
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if (mindist > dist) {
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mindist = dist;
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result[0] = a;
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result[1] = b;
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}
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}
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}
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return mindist;
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}
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static long dist(Point a, Point b) {
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long dx = a.x - b.x;
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long dy = a.y - b.y;
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return dx * dx + dy * dy;
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}
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// random test
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public static void main(String[] args) {
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Random rnd = new Random();
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for (int step = 0; step < 10_000; step++) {
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int n = 100;
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Point[] points = new Point[n];
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for (int i = 0; i < n; i++) {
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points[i] = new Point(rnd.nextInt(1000) - 500, rnd.nextInt(1000) - 500);
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}
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Point[] p = findClosestPair(points);
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long res1 = dist(p[0], p[1]);
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long res2 = slowClosestPair(points);
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if (res1 != res2)
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throw new RuntimeException(res1 + " " + res2);
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}
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}
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static long slowClosestPair(Point[] points) {
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long res = Long.MAX_VALUE;
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for (int i = 0; i < points.length; i++)
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for (int j = i + 1; j < points.length; j++)
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res = Math.min(res, dist(points[i], points[j]));
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return res;
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}
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}
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