import java.util.*;

public class Subsets {
    public static void main(String[] args) {
        List<String> names = new LinkedList<String>();
        names.add("Janet");
        names.add("Robert");
        names.add("Morgan");
        names.add("Char");

        subsets(names);
    }
    
    // Prints all sub-lists of the given list of Strings.
    // Precondition: elements != null and elements contains no duplicates
    public static void subsets(List<String> elements) {
        List<String> chosen = new ArrayList<String>();
        explore(elements, chosen);
    }
    
    // Private recursive helper to explore all sub-lists of the given list of
    // elements, assuming the given list of strings have already been chosen.
    private static void explore(List<String> elements, List<String> chosen) {
        if (elements.isEmpty()) {
            System.out.println(chosen);   // base case; nothing left to choose
        } else {
            String first = elements.remove(0);   // make a choice: 1st element
            
            // two explorations: one with this first element, one without
            chosen.add(first);
            explore(elements, chosen);
            chosen.remove(chosen.size() - 1);
            explore(elements, chosen);
            
            elements.add(0, first);        // backtrack!  put 1st element back
        }
    }
}