org.apache.commons.collections4.iterators
Class PermutationIterator<E>

java.lang.Object
  org.apache.commons.collections4.iterators.PermutationIterator<E>

Type Parameters:

E - the type of the objects being permuted

All Implemented Interfaces:

Iterator<List<E>>

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

This iterator creates permutations of an input collection, using the Steinhaus-Johnson-Trotter algorithm (also called plain changes).

The iterator will return exactly n! permutations of the input collection. The remove() operation is not supported, and will throw an UnsupportedOperationException.

NOTE: in case an empty collection is provided, the iterator will return exactly one empty list as result, as 0! = 1.

Since:

4.0

Version:

$Id: PermutationIterator.java 1477802 2013-04-30 20:01:28Z tn $

PermutationIterator

public PermutationIterator(Collection<E> coll)

Standard constructor for this class.

Parameters:

coll - the collection to generate permutations for

Throws:

NullPointerException - if coll is null

hasNext

public boolean hasNext()

Indicates if there are more permutation available.

Specified by:

hasNext in interface Iterator<List<E>>

Returns:

true if there are more permutations, otherwise false

next

public List<E> next()

Returns the next permutation of the input collection.

Specified by:

next in interface Iterator<List<E>>

Returns:

a list of the permutator's elements representing a permutation

Throws:

NoSuchElementException - if there are no more permutations

remove

public void remove()

Specified by:

remove in interface Iterator<List<E>>