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Very simple java library to generate permutations, combinations and other combinatorial sequences.

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/**
 * Combinatorics Library
 * Copyright 2012 Dmytro Paukov [email protected]
 */
package org.paukov.combinatorics;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * This is a special abstract class for all integer generators.
 *
 * There is a general pattern how to use the integer generators.
 *
 *  * // create an integer vector
 * IntegerVector vector = new IntegerVector(new int[] { elements });
 *
 * // create a concrete integer generator
 * IntegerGenerator generator = IntegerFactory.create < Concrete > Generator(vector);
 *
 * // Iterate the generated objects
 * for (IntegerVector v : generator) {
 * 	System.out.println(v);
 * }
 * 
 *
 * @author Dmytro Paukov
 * @version 2.0
 * @see IntegerVector
 * @see IntegerFactory
 * @see IGenerator
 */
public abstract class IntegerGenerator implements IGenerator {

  /**
   * Returns all generated vectors as a list
   *
   * @return List of all generated objects/vectors
   */
  @Override
  public List generateAllObjects() {
    return generateFilteredObjects(null);
  }

  /**
   * Returns the generated vectors filtered by a filter
   *
   * @param filter The filter to be applied to the generated result
   * @return The list of the filtered vectors
   * @see IFilter
   */
  @Override
  public List generateFilteredObjects(
      IFilter filter) {
    List list = new ArrayList();
    long index = 0;
    for (IntegerVector vector : this) {
      if (filter == null || filter.accepted(index, vector)) {
        list.add(vector);
      }
      index++;
    }
    return list;
  }

  /**
   * Returns vectors as a list for specified range of indexes (from the
   * startIndex to stopIndex)
   *
   * @return List of the generated objects/vectors
   */
  @Override
  public List generateObjectsRange(long startIndex,
      long stopIndex) {
    assert (startIndex <= stopIndex);
    List list = new ArrayList();
    Iterator iterator = this.iterator();
    int index = 1;
    while (iterator.hasNext()) {
      if (index >= startIndex && index <= stopIndex) {
        list.add(iterator.next());
      } else if (index > stopIndex) {
        return list;
      } else {
        iterator.next();
      }
      index++;
    }
    return list;
  }

}