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Simple java library to generate permutations, combinations and other combinatorial sequences

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/*
 * Combinatorics Library 3
 * Copyright 2009-2016 Dmytro Paukov [email protected]
 */
package org.paukov.combinatorics3;

import static org.paukov.combinatorics3.PermutationGenerator.hasDuplicates;

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

/**
 * This generator generates all possible permutations of the specified initial
 * vector
 * 
 * A permutation is an ordering of a set in the context of all possible
 * orderings. For example, the set containing the first three digits, 123, has
 * six permutations: 123, 132, 213, 231, 312, and 321.
 * 

 * This is an example of the permutations of 3 string items (apple, orange,
 * cherry):
 * 

 * 

 *
 *  *
 * // Create the initial vector of 3 elements (apple, orange, cherry)
 * ICombinatoricsVector<String> originalVector = Factory
 * 		.createVector(new String[] { "apple", "orange", "cherry" });
 *
 * // Create the permutation generator by calling the appropriate method in the
 * // Factory class
 * Generator<String> gen = Factory.createPermutationGenerator(originalVector);
 *
 * // Print the result
 * for (ICombinatoricsVector<String> perm : gen)
 * 	System.out.println(perm);
 *
 * 
 *
 * 
 * 
 * And the result
 * 

 * 

 *
 *  *   CombinatoricsVector=([apple, orange, cherry], size=3)
 *   CombinatoricsVector=([apple, cherry, orange], size=3)
 *   CombinatoricsVector=([cherry, apple, orange], size=3)
 *   CombinatoricsVector=([cherry, orange, apple], size=3)
 *   CombinatoricsVector=([orange, cherry, apple], size=3)
 *   CombinatoricsVector=([orange, apple, cherry], size=3)
 * 
 *
 * 
 * 
 *
 * @param  Type of the elements in the permutations
 * @author Dmytro Paukov
 * @version 2.0
 */
class SimplePermutationGenerator implements IGenerator> {

  final boolean hasDuplicates;
  final boolean treatAsIdentical;
  final List originalVector;

  /**
   * Constructor
   *
   * @param vector Vector which is used for permutation generation
   * @param treatAsIdentical True if the generator should treat the vector as identical
   */
  SimplePermutationGenerator(Collection vector,
      boolean treatAsIdentical) {
    this.hasDuplicates = hasDuplicates(vector);
    this.treatAsIdentical = treatAsIdentical;
    this.originalVector = new ArrayList<>(vector);
  }

  @Override
  public Iterator> iterator() {
    if (isDuplicateIterator()) {
      return new DuplicatedPermutationIterator<>(this);
    } else {
      return new SimplePermutationIterator<>(this);
    }
  }

  private boolean isDuplicateIterator() {
    return (!treatAsIdentical && hasDuplicates);
  }
}