permutations/combinatorics library for java? [closed]

Answer 1

Have you checked Guava? It seems to offer permutations in Collections2

Class Collections2
permutations(Collection elements)
Returns a Collection of all the permutations of the specified Collection.

Answer 2

There's the PermutationIterator class in the Apache Commons Collection library version 4. It accepts a generic Collection and provides an Iterator that iterates over all permutations of the elements in the Collection (each call to next() on the Iterator provides an ordered List).

I just realised version 4 of the Collection library was only released on 2013-11-27. Version 3 doesn't provide a utility for permutations. V4 "represents a major revamp of collections by supporting new language features introduced with Java 1.5, mainly support for generics."