最近点对(Java实现)

标签：最近点对   java   

最近点对问题：

在二维平面上的n个点中，快速的最近的一对点的距离。

java实现：

package p2;

import static java.lang.Math.*;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;

public class CloestPair {
	// 坐标点
	static class Point {
		public Point() {
		}

		public Point(double x, double y) {
			this.x = x;
			this.y = y;
		}
		double x;
		double y;
	}

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		while (true) {
			int n = scanner.nextInt();
			Point[] ps = new Point[n];
			for (int i = 0; i < n; i++) {
				double x = scanner.nextDouble();
				double y = scanner.nextDouble();
				ps[i] = new Point(x, y);
			}
			// 按照X轴坐标升序排序
			Arrays.sort(ps, new Comparator<Point>() {
				@Override
				public int compare(Point o1, Point o2) {
					if (o1.x < o2.x)
						return -1;
					if (o1.x > o2.x)
						return 1;
					if (o1.y < o2.y)
						return -1;
					if (o1.y > o2.y)
						return 1;
					return 0;
				}
			});
			double minDis = minDistance(ps, 0, n - 1);
			System.out.println(minDis);
		}

	}

	/**
	 * 点对之间的最小距离
	 * 
	 * @param ps
	 * @param l
	 * @param r
	 * @return
	 */
	public static double minDistance(Point[] ps, int l, int r) {
		/**
		 * 同一个点,不存在点对,距离不能取0,返回最大值
		 */
		if (l == r) {
			return Double.MAX_VALUE;
		}
		if (l + 1 == r) {
			return distance(ps[l], ps[r]);
		}
		int center = l + (r - l) / 2;
		double dis1 = minDistance(ps, l, center);
		double dis2 = minDistance(ps, center + 1, r);
		double minDis = min(dis1, dis2);
		ArrayList<Point> nearPoints = new ArrayList<>();
		// 选出距离中间线小于minDis的点
		for (Point p : ps) {
			if (abs(ps[center].x - p.x) <= minDis) {
				nearPoints.add(p);
			}
		}
		// 按照Y轴升序排序
		Collections.sort(nearPoints, new Comparator<Point>() {
			@Override
			public int compare(Point o1, Point o2) {
				if (o1.y < o2.y)
					return -1;
				if (o1.y > o2.y)
					return 1;
				if (o1.x < o2.x)
					return -1;
				if (o1.x > o2.x)
					return 1;
				return 0;
			}
		});
		for (int i = 0; i < nearPoints.size(); i++) {
			for (int j = i + 1; j < nearPoints.size(); j++) {
				if (nearPoints.get(j).y - nearPoints.get(i).y > minDis) {
					break;// 元素y+1离元素i更远,没必要继续比较
				}
				double d = distance(nearPoints.get(j), nearPoints.get(i));
				if (d < minDis) {
					minDis = d;
				}
			}
		}
		return minDis;
	}

	public static double distance(Point p1, Point p2) {
		if (p1 == p2)
			return 0;
		return sqrt(pow(p1.x - p2.x, 2) + pow(p1.y - p2.y, 2));
	}

}

最近点对(Java实现)

标签：最近点对   java   

原文地址：http://blog.csdn.net/u010786672/article/details/44683439