Find all subsets of length k in an array

Question

Given a set {1,2,3,4,5...n} of n elements, we need to find all subsets of length k .

For example, if n = 4 and k = 2, the output would be

Answer 1

If you are looking for Iterator pattern answer then here you go.

public static  Iterable> getList(final Iterable list) {

    List> listOfList = new ArrayList<>();

    for (T t: list)
        listOfList.add(Collections.singletonList(t));

    return listOfList;
}
public static  Iterable> getIterable(final Iterable list, final int size) {

    final List vals = new ArrayList<>();
    int numElements = 0;
    for (T t : list) {
        vals.add(t);
        numElements++;
    }

    if (size == 1) {
        return getList(vals);
    }
    if (size == numElements) {
        return Collections.singletonList(vals);
    }

    return new Iterable>() {

        @Override
        public Iterator> iterator() {
            return new Iterator>() {

                int currPos = 0;                    
                Iterator> nextIterator = getIterable(
                    vals.subList(this.currPos + 1, vals.size()), size - 1).iterator();

                @Override
                public boolean hasNext() {
                    if ((this.currPos < vals.size()-2) && (this.currPos+size < vals.size()))
                        return true;
                    return false;
                }

                @Override
                public List next() {
                    if (!nextIterator.hasNext()) {
                        this.currPos++;
                        nextIterator = getIterable(vals.subList(this.currPos+1, vals.size()), size-1).iterator();
                    }
                    final List ret = new ArrayList<>(nextIterator.next());
                    ret.add(0, vals.get(this.currPos));
                    return ret;
                }
            };
        }
    };
}