org.xhtmlrenderer.util

Class PermutationGenerator

java.lang.Object

org.xhtmlrenderer.util.PermutationGenerator

public class PermutationGenerator
extends Object

The PermutationGenerator Java class systematically generates permutations. It relies on the fact that any set with n elements can be placed in one-to-one correspondence with the set {1, 2, 3, ..., n}. The algorithm is described by Kenneth H. Rosen, Discrete Mathematics and Its Applications, 2nd edition (NY: McGraw-Hill, 1991), pp. 282-284.

The class is very easy to use. Suppose that you wish to generate all permutations of the strings "a", "b", "c", and "d". Put them into an array. Keep calling the permutation generator's () method until there are no more permutations left. The () method returns an array of integers, which tell you the order in which to arrange your original array of strings. Here is a snippet of code which illustrates how to use the PermutationGenerator class.

 int[] indices;
 String[] elements = {"a", "b", "c", "d"};
 PermutationGenerator x = new PermutationGenerator (elements.length);
 StringBuilder permutation;
 while (x.hasMore ()) {
 permutation = new StringBuilder ();
 indices = x.getNext ();
 for (int i = 0; i < indices.length; i++) {
 permutation.append (elements[indices[i]]);
 }
 System.out.println (permutation.toString ());
 }
 

One caveat. Don't use this class on large sets. Recall that the number of permutations of a set containing n elements is n factorial, which is a very large number even when n is as small as 20. 20! is 2,432,902,008,176,640,000.

NOTE: This class was taken from the internet, as posted by Michael Gilleland on this website. The code was posted with the following comment: "The source code is free for you to use in whatever way you wish."

Author:

Michael Gilleland, Merriam Park Software (http://www.merriampark.com/index.htm)

Constructor Summary

Constructors

Constructor and Description
PermutationGenerator(int n)

Method Summary

Modifier and Type	Method and Description
int[]	getNext()
BigInteger	getNumLeft()
BigInteger	getTotal()
boolean	hasMore()
void	reset()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PermutationGenerator

public PermutationGenerator(int n)

Method Detail

reset

public void reset()

getNumLeft

public BigInteger getNumLeft()

getTotal

public BigInteger getTotal()

hasMore

public boolean hasMore()

getNext

public int[] getNext()