Dijkstra.java

package id.ac.itats.skripsi.shortestpath.engine;

import id.ac.itats.skripsi.shortestpath.model.Edge;
import id.ac.itats.skripsi.shortestpath.model.Graph;
import id.ac.itats.skripsi.shortestpath.model.Vertex;

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

public class Dijkstra {
	
	public void computePaths(Graph graph, Vertex source) {
	
		if (! graph.hasClearTree) {
			graph.clearTree();
		}	
		
		System.out.println(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);
				}
			}
		}
		
		graph.hasClearTree = false;
	}

	public 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;
	}

}