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Created April 2, 2013 21:25
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Djikstra's algorithm implmentation
mport 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("Redvile");
Vertex v1 = new Vertex("Blueville");
Vertex v2 = new Vertex("Greenville");
Vertex v3 = new Vertex("Orangeville");
Vertex v4 = new Vertex("Purpleville");
v0.adjacencies = new Edge[]{ new Edge(v1, 5),
new Edge(v2, 10),
new Edge(v3, 8) };
v1.adjacencies = new Edge[]{ new Edge(v0, 5),
new Edge(v2, 3),
new Edge(v4, 7) };
v2.adjacencies = new Edge[]{ new Edge(v0, 10),
new Edge(v1, 3) };
v3.adjacencies = new Edge[]{ new Edge(v0, 8),
new Edge(v4, 2) };
v4.adjacencies = new Edge[]{ new Edge(v1, 7),
new Edge(v3, 2) };
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);
}
}
}
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