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/*
 * (C) Copyright 2008-2018, by Andrew Newell 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 hyper cube graph of
 * any size. This is a graph that can be represented by bit strings, so for an n-dimensional
 * hypercube each vertex resembles an n-length bit string. Then, two vertices are adjacent if and
 * only if their bitstring differ by exactly one element.
 * 
 * @param  the graph vertex type
 * @param  the graph edge type
 *
 * @author Andrew Newell
 * @since Dec 21, 2008
 */
public class HyperCubeGraphGenerator
    implements
    GraphGenerator
{
    private int dim;

    /**
     * Creates a new generator
     *
     * @param dim the dimension of the hypercube
     */
    public HyperCubeGraphGenerator(int dim)
    {
        this.dim = dim;
    }

    @Override
    public void generateGraph(Graph target, Map resultMap)
    {
        // Vertices are created, and they are included in the resultmap as their
        // bitstring representation
        int order = (int) Math.pow(2, dim);
        LinkedList vertices = new LinkedList<>();
        for (int i = 0; i < order; i++) {
            V newVertex = target.addVertex();

            vertices.add(newVertex);
            if (resultMap != null) {
                StringBuilder s = new StringBuilder(Integer.toBinaryString(i));
                while (s.length() < dim) {
                    s.insert(0, "0");
                }
                resultMap.put(s.toString(), newVertex);
            }
        }

        // Two vertices will have an edge if their bitstrings differ by exactly
        // 1 element
        for (int i = 0; i < order; i++) {
            for (int j = i + 1; j < order; j++) {
                for (int z = 0; z < dim; z++) {
                    if ((j ^ i) == (1 << z)) {
                        target.addEdge(vertices.get(i), vertices.get(j));
                        break;
                    }
                }
            }
        }
    }
}

// End HyberCubeGraphGenerator.java