dijkstra.java

一个基于JAVA的Dijkstra算法程序,可用于仿真中作为路由算法的一个组件.包含网络拓扑及使用方法的代码.

/* Copyright (c) 2008 the authors listed at the following URL, and/or
the authors of referenced articles or incorporated external code:
http://en.literateprograms.org/Dijkstra's_algorithm_(Java)?action=history&offset=20080816175957

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The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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Retrieved from: http://en.literateprograms.org/Dijkstra's_algorithm_(Java)?oldid=14309
*/

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 Dijkstra
{
    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("Harrisburg");
	Vertex v1 = new Vertex("Baltimore");
	Vertex v2 = new Vertex("Washington");
	Vertex v3 = new Vertex("Philadelphia");
	Vertex v4 = new Vertex("Binghamton");
	Vertex v5 = new Vertex("Allentown");
	Vertex v6 = new Vertex("New York");
	v0.adjacencies = new Edge[]{ new Edge(v1,  79.83),
	                             new Edge(v5,  81.15) };
	v1.adjacencies = new Edge[]{ new Edge(v0,  79.75),
	                             new Edge(v2,  39.42),
	                             new Edge(v3, 103.00) };
	v2.adjacencies = new Edge[]{ new Edge(v1,  38.65) };
	v3.adjacencies = new Edge[]{ new Edge(v1, 102.53),
	                             new Edge(v5,  61.44),
	                             new Edge(v6,  96.79) };
	v4.adjacencies = new Edge[]{ new Edge(v5, 133.04) };
	v5.adjacencies = new Edge[]{ new Edge(v0,  81.77),
	                             new Edge(v3,  62.05),
	                             new Edge(v4, 134.47),
	                             new Edge(v6,  91.63) };
	v6.adjacencies = new Edge[]{ new Edge(v3,  97.24),
	                             new Edge(v5,  87.94) };
	Vertex[] vertices = { v0, v1, v2, v3, v4, v5, v6 };


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

    }
}