be-graphes/src/main/org/insa/algo/weakconnectivity/WeaklyConnectedComponentsAlgorithm.java

package org.insa.algo.weakconnectivity;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

import org.insa.algo.AbstractAlgorithm;
import org.insa.algo.AbstractSolution.Status;
import org.insa.graph.Arc;
import org.insa.graph.Graph;
import org.insa.graph.Node;

public class WeaklyConnectedComponentsAlgorithm
        extends AbstractAlgorithm<WeaklyConnectedComponentObserver> {

    /**
     * @param data Input data for this algorithm.
     */
    public WeaklyConnectedComponentsAlgorithm(WeaklyConnectedComponentsData data) {
        super(data);
    }

    @Override
    public WeaklyConnectedComponentsSolution run() {
        return (WeaklyConnectedComponentsSolution) super.run();
    }

    @Override
    public WeaklyConnectedComponentsData getInputData() {
        return (WeaklyConnectedComponentsData) super.getInputData();
    }

    /**
     * Notify all observers that the algorithm is entering a new component.
     * 
     * @param curNode Starting node for the component.
     */
    protected void notifyStartComponent(Node curNode) {
        for (WeaklyConnectedComponentObserver obs: getObservers()) {
            obs.notifyStartComponent(curNode);
        }
    }

    /**
     * Notify all observers that a new node has been found for the current
     * component.
     * 
     * @param node New node found for the current component.
     */
    protected void notifyNewNodeInComponent(Node node) {
        for (WeaklyConnectedComponentObserver obs: getObservers()) {
            obs.notifyNewNodeInComponent(node);
        }
    }

    /**
     * Notify all observers that the algorithm has computed a new component.
     * 
     * @param nodes List of nodes in the component.
     */
    protected void notifyEndComponent(ArrayList<Node> nodes) {
        for (WeaklyConnectedComponentObserver obs: getObservers()) {
            obs.notifyEndComponent(nodes);
        }
    }

    /**
     * @return An adjacency list for the undirected graph equivalent to the stored
     *         graph.
     */
    protected ArrayList<HashSet<Integer>> createUndirectedGraph() {
        int nNodes = getInputData().getGraph().getNodes().size();
        ArrayList<HashSet<Integer>> res = new ArrayList<HashSet<Integer>>(nNodes);
        for (int i = 0; i < nNodes; ++i) {
            res.add(new HashSet<Integer>());
        }

        for (Node node: getInputData().getGraph().getNodes()) {
            for (Arc arc: node.getSuccessors()) {
                res.get(node.getId()).add(arc.getDestination().getId());
                if (arc.getRoadInformation().isOneWay()) {
                    res.get(arc.getDestination().getId()).add(node.getId());
                }
            }
        }

        return res;
    }

    /**
     * Apply a breadth first search algorithm on the given undirected graph
     * (adjacency list), starting at node cur, and marking nodes in marked.
     * 
     * @param marked
     * @param cur
     * 
     * @return
     */
    protected ArrayList<Node> bfs(ArrayList<HashSet<Integer>> ugraph, boolean[] marked, int cur) {
        List<Node> nodes = getInputData().getGraph().getNodes();
        ArrayList<Node> component = new ArrayList<Node>();

        // Using a queue because we are doing a BFS
        Queue<Integer> queue = new LinkedList<Integer>();

        // Notify observers about the current component.
        notifyStartComponent(nodes.get(cur));

        // Add original node and loop until the queue is empty.
        queue.add(cur);
        marked[cur] = true;
        while (!queue.isEmpty()) {
            Node node = nodes.get(queue.remove());
            component.add(node);

            // Notify observers
            notifyNewNodeInComponent(node);

            for (Integer destId: ugraph.get(node.getId())) {
                Node dest = nodes.get(destId);
                if (!marked[dest.getId()]) {
                    queue.add(destId);
                    marked[destId] = true;
                }
            }
        }

        notifyEndComponent(component);

        return component;
    }

    @Override
    protected WeaklyConnectedComponentsSolution doRun() {

        Graph graph = getInputData().getGraph();
        ArrayList<HashSet<Integer>> ugraph = createUndirectedGraph();
        boolean[] marked = new boolean[graph.getNodes().size()];
        Arrays.fill(marked, false);

        ArrayList<ArrayList<Node>> components = new ArrayList<ArrayList<Node>>();

        // perform algorithm
        int cur = 0;
        while (cur < marked.length) {
            // Apply BFS
            components.add(this.bfs(ugraph, marked, cur));

            // Find next non-marked
            for (; cur < marked.length && marked[cur]; ++cur)
                ;
        }

        return new WeaklyConnectedComponentsSolution(getInputData(), Status.OPTIMAL, components);
    }

}