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);
 StringBuffer permutation;
 while (x.hasMore ()) {
 permutation = new StringBuffer ();
 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 Details

    • PermutationGenerator

      public PermutationGenerator(int n)
  • Method Details

    • reset

      public void reset()
    • getNumLeft

      public BigInteger getNumLeft()
    • getTotal

      public BigInteger getTotal()
    • hasMore

      public boolean hasMore()
    • getNext

      public int[] getNext()