Dijkstra's Algorithm in Java

Question

I've been trying to use Dijkstra's Algorithm to find the shortest path in a set of vertices in Java. I've found code for when people have preset values, but I haven't managed to find anything involving files that have matrices read in. Here's the code I currently have:

import java.util.*;

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)
    {
        // mark all the vertices 
        Vertex A = new Vertex("A");
        Vertex B = new Vertex("B");
        Vertex D = new Vertex("D");
        Vertex F = new Vertex("F");
        Vertex K = new Vertex("K");
        Vertex J = new Vertex("J");
        Vertex M = new Vertex("M");
        Vertex O = new Vertex("O");
        Vertex P = new Vertex("P");
        Vertex R = new Vertex("R");
        Vertex Z = new Vertex("Z");

        // set the edges and weight
        A.adjacencies = new Edge[]{ new Edge(M, 8) };
        B.adjacencies = new Edge[]{ new Edge(D, 11) };
        D.adjacencies = new Edge[]{ new Edge(B, 11) };
        F.adjacencies = new Edge[]{ new Edge(K, 23) };
        K.adjacencies = new Edge[]{ new Edge(O, 40) };
        J.adjacencies = new Edge[]{ new Edge(K, 25) };
        M.adjacencies = new Edge[]{ new Edge(R, 8) };
        O.adjacencies = new Edge[]{ new Edge(K, 40) };
        P.adjacencies = new Edge[]{ new Edge(Z, 18) };
        R.adjacencies = new Edge[]{ new Edge(P, 15) };
        Z.adjacencies = new Edge[]{ new Edge(P, 18) };


        computePaths(A); // run Dijkstra
        System.out.println("Distance to " + Z + ": " + Z.minDistance);
        List<Vertex> path = getShortestPathTo(Z);
        System.out.println("Path: " + path);
    }
}

I need to make it be able to read in a matrix of any size in the form of a .csv file and use the algorithm to find the path.

One of the sample files looks like this:

0,5,0,5,0,0,0,0,0
5,0,5,0,8,0,0,0,0
0,5,0,0,0,1,0,0,0
5,0,0,0,6,0,0,0,0
0,8,0,6,0,2,0,0,0
0,0,1,0,2,0,0,0,6
0,0,0,0,0,0,0,0,0
0,0,0,0,0,0,0,0,9
0,0,0,0,0,6,0,9,0

The file name is NineUnDirected.csv. The largest sample I have to read in has 100 vertices.

I'd appreciate any help you could give me as to reading in the file and running it through the program.

Answer 1

Scanner scanner = new Scanner(new File("NineUnDirected.csv"));
List<Integer> matrix = new ArrayList<>();
while(scanner.hasNextInt()){
   matrix.add(scanner.nextInt());
}

And then you can convert matrix in a more convenient form, if it is neccessary.