UndirectedSparseGraph.java

/*
 * Created on Apr 1, 2007
 *
 * Copyright (c) 2007, the JUNG Project and the Regents of the University 
 * of California
 * All rights reserved.
 *
 * This software is open-source under the BSD license; see either
 * "license.txt" or
 * http://jung.sourceforge.net/license.txt for a description.
 */
package edu.uci.ics.jung.graph;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.collections15.Factory;

import edu.uci.ics.jung.graph.util.EdgeType;
import edu.uci.ics.jung.graph.util.Pair;

/**
 * An implementation of <code>UndirectedGraph</code> that is suitable
 * for sparse graphs.
 */
@SuppressWarnings("serial")
public class UndirectedSparseGraph<V, E> extends AbstractTypedGraph<V, E>
        implements UndirectedGraph<V, E>
{

    /**
     * Returns a {@code Factory} that creates an instance of this graph type.
     * @param <V> the vertex type for the graph factory
     * @param <E> the edge type for the graph factory
     */
    public static <V,E> Factory<UndirectedGraph<V,E>> getFactory() {
        return new Factory<UndirectedGraph<V,E>> () {

            public UndirectedGraph<V,E> create() {
                return new UndirectedSparseGraph<V,E>();
            }
        };
    }

    protected Map<V, Map<V,E>> vertices; // Map of vertices to adjacency maps of vertices to incident edges
    protected Map<E, Pair<V>> edges;    // Map of edges to incident vertex sets

    /**
     * Creates an instance.
     */
    public UndirectedSparseGraph() {
    	super(EdgeType.UNDIRECTED);
        vertices = new HashMap<V, Map<V,E>>();
        edges = new HashMap<E, Pair<V>>();
    }

    @Override
    public boolean addEdge(E edge, Pair<? extends V> endpoints, EdgeType edgeType)
    {
    	this.validateEdgeType(edgeType);
        Pair<V> new_endpoints = getValidatedEndpoints(edge, endpoints);
        if (new_endpoints == null)
            return false;
        
        V v1 = new_endpoints.getFirst();
        V v2 = new_endpoints.getSecond();
        
        if (findEdge(v1, v2) != null)
            return false;
        
        edges.put(edge, new_endpoints);

        if (!vertices.containsKey(v1))
            this.addVertex(v1);
        
        if (!vertices.containsKey(v2))
            this.addVertex(v2);
        
        // map v1 to <v2, edge> and vice versa
        vertices.get(v1).put(v2, edge);
        vertices.get(v2).put(v1, edge);

        return true;
    }

    public Collection<E> getInEdges(V vertex)
    {
        return this.getIncidentEdges(vertex);
    }

    public Collection<E> getOutEdges(V vertex)
    {
        return this.getIncidentEdges(vertex);
    }

    public Collection<V> getPredecessors(V vertex)
    {
        return this.getNeighbors(vertex);
    }

    public Collection<V> getSuccessors(V vertex)
    {
        return this.getNeighbors(vertex);
    }

    @Override
    public E findEdge(V v1, V v2)
    {
        if (!containsVertex(v1) || !containsVertex(v2))
            return null;
        return vertices.get(v1).get(v2);
    }
    
    @Override
    public Collection<E> findEdgeSet(V v1, V v2)
    {
        if (!containsVertex(v1) || !containsVertex(v2))
            return null;
        ArrayList<E> edge_collection = new ArrayList<E>(1);
//        if (!containsVertex(v1) || !containsVertex(v2))
//            return edge_collection;
        E e = findEdge(v1, v2);
        if (e == null)
            return edge_collection;
        edge_collection.add(e);
        return edge_collection;
    }
    
    public Pair<V> getEndpoints(E edge)
    {
        return edges.get(edge);
    }

    public V getSource(E directed_edge)
    {
        return null;
    }

    public V getDest(E directed_edge)
    {
        return null;
    }

    public boolean isSource(V vertex, E edge)
    {
        return false;
    }

    public boolean isDest(V vertex, E edge)
    {
        return false;
    }

    public Collection<E> getEdges()
    {
        return Collections.unmodifiableCollection(edges.keySet());
    }

    public Collection<V> getVertices()
    {
        return Collections.unmodifiableCollection(vertices.keySet());
    }

    public boolean containsVertex(V vertex)
    {
        return vertices.containsKey(vertex);
    }

    public boolean containsEdge(E edge)
    {
        return edges.containsKey(edge);
    }

    public int getEdgeCount()
    {
        return edges.size();
    }

    public int getVertexCount()
    {
        return vertices.size();
    }

    public Collection<V> getNeighbors(V vertex)
    {
        if (!containsVertex(vertex))
            return null;
        return Collections.unmodifiableCollection(vertices.get(vertex).keySet());
    }

    public Collection<E> getIncidentEdges(V vertex)
    {
        if (!containsVertex(vertex))
            return null;
        return Collections.unmodifiableCollection(vertices.get(vertex).values());
    }

    public boolean addVertex(V vertex)
    {
        if(vertex == null) {
            throw new IllegalArgumentException("vertex may not be null");
        }
        if (!containsVertex(vertex)) {
            vertices.put(vertex, new HashMap<V,E>());
            return true;
        } else {
            return false;
        }
    }

    public boolean removeVertex(V vertex)
    {
        if (!containsVertex(vertex))
            return false;

        // iterate over copy of incident edge collection
        for (E edge : new ArrayList<E>(vertices.get(vertex).values()))
            removeEdge(edge);
        
        vertices.remove(vertex);
        return true;
    }

    public boolean removeEdge(E edge)
    {
        if (!containsEdge(edge))
            return false;
        
        Pair<V> endpoints = getEndpoints(edge);
        V v1 = endpoints.getFirst();
        V v2 = endpoints.getSecond();
        
        // remove incident vertices from each others' adjacency maps
        vertices.get(v1).remove(v2);
        vertices.get(v2).remove(v1);

        edges.remove(edge);
        return true;
    }
}