groovy.util
Class PermutationGenerator<E>

java.lang.Object
  groovy.util.PermutationGenerator<E>

All Implemented Interfaces:

Iterator<List<E>>

public class PermutationGenerator<E>
extends Object
implements Iterator<List<E>>

Systematically generate permutations. Adapted from Java Code by Michael Gilleland (released with no restrictions) using an algorithm described here: Kenneth H. Rosen, Discrete Mathematics and Its Applications, 2nd edition (NY: McGraw-Hill, 1991), pp. 282-284

Constructor Summary

PermutationGenerator(Collection<E> items)
WARNING: Don't make n too large.

Method Summary

BigInteger	getTotal()
boolean	hasNext()
List<E>	next() Generate next permutation (algorithm from Rosen p. 284)
void	remove()
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(Collection<E> items)

WARNING: Don't make n too large. Recall that the number of permutations is n! which can be very large, even when n is as small as 20 -- 20! = 2,432,902,008,176,640,000 and 21! is too big to fit into a Java long, which is why we use BigInteger instead.

Parameters:

items - the items to permute

Method Detail

reset

public void reset()

getTotal

public BigInteger getTotal()

hasNext

public boolean hasNext()

Specified by:

hasNext in interface Iterator<List<E>>

next

public List<E> next()

Generate next permutation (algorithm from Rosen p. 284)

Specified by:

next in interface Iterator<List<E>>

Returns:

the items permuted

remove

public void remove()

Specified by:

remove in interface Iterator<List<E>>