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/*
 * (C) Copyright 2011-2018, by Assaf Mizrachi and Contributors.
 *
 * JGraphT : a free Java graph-theory library
 *
 * 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.
 */
package org.jgrapht.generate;

import org.jgrapht.*;

import java.util.*;

/**
 * Generates a bidirectional grid graph 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.
 *
 * @param  the graph vertex type
 * @param  the graph edge type
 *
 * @author Assaf Mizrachi
 * @since Dec 29, 2010
 */
public class GridGraphGenerator
    implements
    GraphGenerator
{
    /**
     * 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 target, Map resultMap)
    {
        Map map = new TreeMap<>();

        // Adding all vertices to the set
        int cornerCtr = 0;
        for (int i = 0; i < (rows * cols); i++) {
            V vertex = target.addVertex();
            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) == j)) || ((i + cols) == j)) {
                    target.addEdge(map.get(i), map.get(j));
                    target.addEdge(map.get(j), map.get(i));
                }
            }
        }
    }
}

// End GridGraphGenerator.java