Question

我的功能是获取一组点，检查它们与给定点的距离，并返回一个最接近点的有序集。如果2点与给定点的距离相同，则两者都会保留，没问题。

我使用该函数从2D坐标中选择任意用户给定点的k个最近点。这只是从有序集中挑选前k个点的问题。

现在它是这样的，我想对于每个添加的点（不好），一次又一次地调用距离计算

import java.awt.geom.Point2D;
import java.util.Comparator;

/**
 * This comparator sorts two points by destination distance.
 */
public class NearestComparator implements Comparator<Point2D> {

    /** The point to be reached. */
    private Point2D destination;

    /**
     * Instantiates a new comparator that sorts points by destination distance, descendant.
     * 
     * @param destination the point to reach
     */
    public NearestComparator(Point2D destination) {
        this.destination = destination;
    }

    /**
     * Sort two points by destination distance, descendant.
     * 
     * @param p1 the first point
     * @param p2 the second point
     */
    @Override
    public int compare(Point2D p1, Point2D p2) {
        double p1_distance = p1.distance(destination);
        double p2_distance = p2.distance(destination);
        return (p1_distance < p2_distance) ? -1 : ((p1_distance > p2_distance) ? 1 : 0);
    }
}

现在的排序代码就像这样

private List<Point2D> getSendOrder(Point2D destination) {
    LinkedList<Point2D> sendOrderList = new LinkedList<Point2D>();
    sendOrderList.add(myPosition);

    Iterator<Point2D> keyIter = neighborLinks.keySet().iterator();
    while (keyIter.hasNext()) {
        sendOrderList.add(keyIter.next());
    }

    // sort list by distance from destination
    Collections.sort(sendOrderList, new NearestComparator(destination));
    return sendOrderList;
}

标准库中是否有数据结构允许我添加一个与其自己的类无关的固定“优先级”的元素？我的意思是，(priority 1, Object ref x)，(priority 2, Object ref y)，(priority 1, Object ref z)等等。

我需要尽可能快地生成尽可能少的垃圾。它用于图中的路由算法。无需快速访问有序集的中间，只需要顶部（最低距离，最高优先级）。但是，能够以有效的方式删除最高优先级元素非常重要。

正如您所看到的，只要我以正确的方式获得一个列表（第一个元素具有更高的优先级等），我就不需要在返回的结果中保留优先级信息。

Answer 1

我已经想过使用Map.Entry包裹距离，如果你需要，这也允许深度复制。

这是一个完整的例子

package sandbox;

import java.awt.geom.Point2D;
import java.util.AbstractMap.SimpleEntry;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Random;

public class Node {

    private Point2D myPosition;
    private Map<Point2D, Node> neighborLinks;

    public class NearestComparator implements Comparator<Entry> {

        @Override
        public int compare(Entry e1, Entry e2) {
            return Double.compare((Double) e1.getValue(), (Double) e2.getValue());
        }
    }

    public List<Point2D> getSendOrder(Point2D destination) {
        LinkedList<Entry> sendOrderList = new LinkedList<>();
        Entry<Point2D, Double> pointWithDist;

        // calculate distance from destination and wrap it using an Entry
        pointWithDist = new SimpleEntry<>(myPosition, myPosition.distance(destination));
        sendOrderList.add(pointWithDist);
        for (Point2D otherPoint : neighborLinks.keySet()) {
            pointWithDist = new SimpleEntry<>(otherPoint, otherPoint.distance(destination));
            sendOrderList.add(pointWithDist);
        }

        // sort list by distance from destination
        Collections.sort(sendOrderList, new NearestComparator());

        // print all the list (debug)
        System.out.println(Arrays.toString(sendOrderList.toArray()));

        // unwrap and deep copy
        LinkedList<Point2D> copiedList = new LinkedList<>();
        Point2D pointToCopy, copiedPoint;
        for (Entry entry : sendOrderList) {
            pointToCopy = (Point2D) entry.getKey();
            copiedPoint = new Point2D.Double(pointToCopy.getX(), pointToCopy.getY());
            copiedList.add(copiedPoint);
        }

        return copiedList;
    }

    public Node(Point2D myPosition, Map<Point2D, Node> neighborLinks) {
        this.myPosition = myPosition;
        this.neighborLinks = neighborLinks;
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Map<Point2D, Node> neighborLinks = new HashMap<>();
        Random rand = new Random();
        double x, y, max = 5;
        for (int i = 0; i < 10; ++i) {
            x = rand.nextDouble() * max;
            y = rand.nextDouble() * max;
            neighborLinks.put(new Point2D.Double(x, y), null);
        }

        Point2D nodePos = new Point2D.Double();
        Node myNode = new Node(nodePos, neighborLinks);

        Point2D destination = new Point2D.Double();
        myNode.getSendOrder(destination);
    }

}

Java快速找到给定2D点的k个最近点

1 个答案: