List Subsets in Groovy (inspired from Java 8 in Action#13.2.4)

gistfile1.txt

def list = [1,4,9]

println subsets(list)

List<List<Integer>> subsets(List<Integer> list) {
    if(!list) {
        return [[]]
    }

    final List<List> directSubs = list.tail().collect {
        return [list.head(), it]
    } + [list.tail()]

    return ([[list.head()]] + directSubs + subsets(list.tail())).unique()
}