Derangement, permutation of integer array where for any i, a[i] != i

Derangement.java

import java.util.*;

public class Derangement {

    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        for (int i=0; i<4; ++i) {
            list.add(i);
        }
        for (List<Integer> li : derangement(list)) {
            System.out.println(li);
        }
    }

    public static <T> List<List<T>> derangement(List<T> elements) {
        List<List<T>> list = new ArrayList<>();
        if (elements.size() == 0) {
            list.add(new ArrayList<T>());
        } else {
            backtrack(elements, new int[elements.size()], 0, new BitSet(elements.size()), list);
        }
        return list;
    }

    private static <T> void backtrack(final List<T> elements,
                                      final int[] buffer,
                                      int k,
                                      BitSet bs,
                                      List<List<T>> result) {
        if (k == elements.size()) {
            List<T> range = new ArrayList<>();
            for (int i : buffer) {
                range.add(elements.get(i));
            }
            result.add(range);
        } else {
            for (int i=0; i<elements.size(); ++i) {
                if (!bs.get(i) && i != k) {
                    bs.set(i);
                    buffer[k] = i;
                    backtrack(elements, buffer, k+1, bs, result);
                    bs.set(i, false);
                }
            }
        }
    }
}