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/*
 * (C) Copyright 2003-2018, by John V Sichi 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 ring graph of any size. A ring graph is a graph that contains a single cycle that
 * passes through all its vertices exactly once. For a directed graph, the generated edges are
 * oriented consistently around the ring.
 *
 * @param  the graph vertex type
 * @param  the graph edge type
 *
 * @author John V. Sichi
 * @since Sep 16, 2003
 */
public class RingGraphGenerator
    implements
    GraphGenerator
{
    private int size;

    /**
     * Construct a new RingGraphGenerator.
     *
     * @param size number of vertices to be generated
     *
     * @throws IllegalArgumentException if the specified size is negative.
     */
    public RingGraphGenerator(int size)
    {
        if (size < 0) {
            throw new IllegalArgumentException("must be non-negative");
        }

        this.size = size;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void generateGraph(Graph target, Map resultMap)
    {
        if (size < 1) {
            return;
        }

        LinearGraphGenerator linearGenerator = new LinearGraphGenerator<>(size);
        Map privateMap = new HashMap<>();
        linearGenerator.generateGraph(target, privateMap);

        V startVertex = privateMap.get(LinearGraphGenerator.START_VERTEX);
        V endVertex = privateMap.get(LinearGraphGenerator.END_VERTEX);
        target.addEdge(endVertex, startVertex);
    }
}

// End RingGraphGenerator.java