GridGraphGenerator.java

/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Creator:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2011, by Barak Naveh and Contributors.
 *
 * This program and the accompanying materials are dual-licensed under
 * either
 *
 * (a) the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation, or (at your option) any
 * later version.
 *
 * or (per the licensee's choosing)
 *
 * (b) the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation.
 */
/* -------------------
 * StarGraphGenerator.java
 * -------------------
 * (C) Copyright 2011-2011, by Assaf Mizrachi and Contributors.
 *
 * Original Author:  Assaf Mizrachi
 * Contributor(s):   -
 *
 * $Id: StarGraphGenerator.java 651 2008-12-24 21:13:41Z perfecthash $
 *
 * Changes
 * -------
 * 3-Jan-2011 : Initial revision (AM);
 *
 */
package org.jgrapht.generate;

import java.util.*;

import org.jgrapht.*;


/**
 * Generates a bidirectional <a
 * href="http://mathworld.wolfram.com/GridGraph.html">grid graph</a> of any
 * size. A grid graph is a two dimensional graph whose vertices correspond to
 * the points in the plane with integer coordinates, x-coordinates being in the
 * range 0,..., n, y-coordinates being in the range 1,...m, and two vertices are
 * connected by an edge whenever the corresponding points are at distance 1.
 * Vertices are created from left to right and from top to bottom.
 *
 * @author Assaf Mizrachi
 * @since Dec 29, 2010
 */
public class GridGraphGenerator<V, E>
    implements GraphGenerator<V, E, V>
{
    

    /**
     * Role for the vertices at the corners.
     */
    public static final String CORNER_VERTEX = "Corner Vertex";

    

    private int rows;

    private int cols;

    

    /**
     * Creates a new GridGraphGenerator object with rows x cols dimension.
     *
     * @param rows the number of rows
     * @param cols the number of columns
     */
    public GridGraphGenerator(int rows, int cols)
    {
        if (rows < 2) {
            throw new IllegalArgumentException(
                "illegal number of rows (" + rows
                + "). there must be at least two.");
        }
        if (cols < 2) {
            throw new IllegalArgumentException(
                "illegal number of columns (" + cols
                + "). there must be at least two.");
        }
        this.rows = rows;
        this.cols = cols;
    }

    

    /**
     * {@inheritDoc}
     */
    @Override public void generateGraph(
        Graph<V, E> target,
        VertexFactory<V> vertexFactory,
        Map<String, V> resultMap)
    {
        Map<Integer, V> map = new TreeMap<Integer, V>();

        // Adding all vertices to the set
        int cornerCtr = 0;
        for (int i = 0; i < (rows * cols); i++) {
            V vertex = vertexFactory.createVertex();
            target.addVertex(vertex);
            map.put(i + 1, vertex);

            boolean isCorner =
                (i == 0) || (i == (cols - 1)) || (i == (cols * (rows - 1)))
                || (i == ((rows * cols) - 1));
            if (isCorner && (resultMap != null)) {
                resultMap.put(CORNER_VERTEX + ' ' + ++cornerCtr, vertex);
            }
        }

        // Iterating twice over the key set, for undirected graph edges are
        // added from upper vertices to lower, and from left to right. The
        // second addEdge call will return nothing; it will not add a the edge
        // at the opposite direction. For directed graph, edges in opposite
        // direction are also added.
        for (int i : map.keySet()) {
            for (int j : map.keySet()) {
                if ((((i % cols) > 0)
                        && ((i + 1) == Integer.valueOf(j)))
                    || ((i + cols) == j))
                {
                    target.addEdge(map.get(i), map.get(j));
                    target.addEdge(map.get(j), map.get(i));
                }
            }
        }
    }
}

// End GridGraphGenerator.java