Question

我正在尝试在JAVA中学习并实现Dijkstra的有向图算法，我通过Stackoverflow找到了这段代码。

http://en.literateprograms.org/index.php?title=Special%3aDownloadCode/Dijkstra%27s_algorithm_%28Java%29&oldid=15444

我理解一些东西，但我很难弄清楚这两个问题的方法是什么？

1）从A开始到A结束的行程次数最多为3次。（这是否意味着我找到了A-A的路线？因为这总是来自0。

这个：路线A-E-B-C-D的距离 - （我应该为每个节点调用计算机然后将它们全部添加起来吗？这是最聪明的方式吗？）

这是我的代码：任何帮助，将不胜感激。

我的输出是：

与A的距离：0.0 路径：[A] 到B的距离：5.0 路径：[A，B] 到C的距离：9.0 路径：[A，B，C] 到D的距离：5.0 路径：[A，D] 到E的距离：7.0 路径：[A，E]

package src.main.java;

import java.util.PriorityQueue;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;

class Vertex implements Comparable<Vertex>
{
    public final String name;
    public Edge[] adjacencies;
    public double minDistance = Double.POSITIVE_INFINITY;
    public Vertex previous;
    public Vertex(String argName) { name = argName; }
    public String toString() { return name; }
    public int compareTo(Vertex other)
    {
        return Double.compare(minDistance, other.minDistance);
    }

}


class Edge
{
    public final Vertex target;
    public final double weight;
    public Edge(Vertex argTarget, double argWeight)
    { target = argTarget; weight = argWeight; }
}

public class Main
{
    public static void computePaths(Vertex source)
    {
        source.minDistance = 0.;
        PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
        vertexQueue.add(source);

        while (!vertexQueue.isEmpty()) {
            Vertex u = vertexQueue.poll();

            // Visit each edge exiting u
            for (Edge e : u.adjacencies)
            {
                Vertex v = e.target;
                double weight = e.weight;
                double distanceThroughU = u.minDistance + weight;
                if (distanceThroughU < v.minDistance) {
                    vertexQueue.remove(v);

                    v.minDistance = distanceThroughU ;
                    v.previous = u;
                    vertexQueue.add(v);
                }
            }
        }
    }

    public static List<Vertex> getShortestPathTo(Vertex target)
    {
        List<Vertex> path = new ArrayList<Vertex>();
        for (Vertex vertex = target; vertex != null; vertex = vertex.previous)
            path.add(vertex);

        Collections.reverse(path);
        return path;
    }

    public static void main(String[] args)
    {
        Vertex v0 = new Vertex("A");
        Vertex v1 = new Vertex("B");
        Vertex v2 = new Vertex("C");
        Vertex v3 = new Vertex("D");
        Vertex v4 = new Vertex("E");
        v0.adjacencies = new Edge[]{ new Edge(v1,  5),
                new Edge(v3,  5), new Edge(v4, 7) };
        v1.adjacencies = new Edge[]{ new Edge(v2,  4)};
        v2.adjacencies = new Edge[]{ new Edge(v3,  8), new Edge(v4, 2) };
        v3.adjacencies = new Edge[]{ new Edge(v2, 8),
                new Edge(v4,  6) };
        v4.adjacencies = new Edge[]{ new Edge(v1, 3) };

        Vertex[] vertices = { v0, v1, v2, v3, v4};

        computePaths(v0);
        for (Vertex v : vertices)
        {
            System.out.println("Distance to " + v + ": " + v.minDistance);
            List<Vertex> path = getShortestPathTo(v);
            System.out.println("Path: " + path);
        }
    }
}

具有有向图java的Dijkstra算法

0 个答案: