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Dijkstra.java

  1 /* Copyright (c) 2010 the authors listed at the following URL, and/or
  2 the authors of referenced articles or incorporated external code:
  3 http://en.literateprograms.org/Dijkstra's_algorithm_(Java)?action=history&offset=20081113161332
  4 
  5 Permission is hereby granted, free of charge, to any person obtaining
  6 a copy of this software and associated documentation files (the
  7 "Software"), to deal in the Software without restriction, including
  8 without limitation the rights to use, copy, modify, merge, publish,
  9 distribute, sublicense, and/or sell copies of the Software, and to
 10 permit persons to whom the Software is furnished to do so, subject to
 11 the following conditions:
 12 
 13 The above copyright notice and this permission notice shall be
 14 included in all copies or substantial portions of the Software.
 15 
 16 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 17 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 18 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 19 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 20 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 21 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 22 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 23 
 24 Retrieved from: http://en.literateprograms.org/Dijkstra's_algorithm_(Java)?oldid=15444
 25 */
 26 
 27 import java.util.PriorityQueue;

 28 
 29 import java.util.List;

 30 import java.util.ArrayList;

 31 import java.util.Collections;

 32 
 33 
 34 class Vertex implements Comparable<Vertex>
 35 {
 36     public final String name;
 37     public Edge[] adjacencies;
 38     public double minDistance = Double.POSITIVE_INFINITY;
 39     public Vertex previous;
 40     public Vertex(String argName) { name = argName; }
 41     public String toString() { return name; }
 42     public int compareTo(Vertex other)
 43     {
 44         return Double.compare(minDistance, other.minDistance);
 45     }
 46 
 47 }
 48 
 49 
 50 class Edge
 51 {
 52     public final Vertex target;
 53     public final double weight;
 54     public Edge(Vertex argTarget, double argWeight)
 55     { target = argTarget; weight = argWeight; }
 56 }
 57 
 58 
 59 public class Dijkstra
 60 {
 61     public static void computePaths(Vertex source)
 62     {
 63         source.minDistance = 0.;
 64         PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
 65 	vertexQueue.add(source);
 66 
 67 	while (!vertexQueue.isEmpty()) {
 68 	    Vertex u = vertexQueue.poll();
 69 
 70             // Visit each edge exiting u

 71             for (Edge e : u.adjacencies)
 72             {
 73                 Vertex v = e.target;
 74                 double weight = e.weight;
 75                 double distanceThroughU = u.minDistance + weight;
 76 		if (distanceThroughU < v.minDistance) {
 77 		    vertexQueue.remove(v);
 78 
 79 		    v.minDistance = distanceThroughU ;
 80 		    v.previous = u;
 81 		    vertexQueue.add(v);
 82 
 83 		}
 84 
 85             }
 86         }
 87     }
 88 
 89 
 90     public static List<Vertex> getShortestPathTo(Vertex target)
 91     {
 92         List<Vertex> path = new ArrayList<Vertex>();
 93         for (Vertex vertex = target; vertex != null; vertex = vertex.previous)
 94             path.add(vertex);
 95 
 96         Collections.reverse(path);
 97         return path;
 98     }
 99 
100     public static void main(String[] args)
101     {
102         Vertex v0 = new Vertex("Harrisburg");
103 	Vertex v1 = new Vertex("Baltimore");
104 	Vertex v2 = new Vertex("Washington");
105 	Vertex v3 = new Vertex("Philadelphia");
106 	Vertex v4 = new Vertex("Binghamton");
107 	Vertex v5 = new Vertex("Allentown");
108 	Vertex v6 = new Vertex("New York");
109 	v0.adjacencies = new Edge[]{ new Edge(v1,  79.83),
110 	                             new Edge(v5,  81.15) };
111 	v1.adjacencies = new Edge[]{ new Edge(v0,  79.75),
112 	                             new Edge(v2,  39.42),
113 	                             new Edge(v3, 103.00) };
114 	v2.adjacencies = new Edge[]{ new Edge(v1,  38.65) };
115 	v3.adjacencies = new Edge[]{ new Edge(v1, 102.53),
116 	                             new Edge(v5,  61.44),
117 	                             new Edge(v6,  96.79) };
118 	v4.adjacencies = new Edge[]{ new Edge(v5, 133.04) };
119 	v5.adjacencies = new Edge[]{ new Edge(v0,  81.77),
120 	                             new Edge(v3,  62.05),
121 	                             new Edge(v4, 134.47),
122 	                             new Edge(v6,  91.63) };
123 	v6.adjacencies = new Edge[]{ new Edge(v3,  97.24),
124 	                             new Edge(v5,  87.94) };
125 	Vertex[] vertices = { v0, v1, v2, v3, v4, v5, v6 };
126 
127 
128         computePaths(v0);
129         for (Vertex v : vertices)
130 	{
131 	    System.out.println("Distance to " + v + ": " + v.minDistance);
132 	    List<Vertex> path = getShortestPathTo(v);
133 	    System.out.println("Path: " + path);
134 	}
135 
136     }
137 }
138


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