Chapter 12, Problem 20E

Explanation of Solution

Method definition:

//All the sub-lists of the given list of Strings gets printed.

/*elements!= null and elements contains no duplicates are the pre-condition*/

//method definition

public static void subsets(List<String> elements)

{

    //define the list

    List<String> chosen = new ArrayList<String>();

    //call the method explore

    explore(elements, chosen);

}

/*Helper recursive function defined to explore all the sub list from the given list of elements, choice is made assuming the given list of string is already chosen*/

//method definition

private static void explore(List<String> elements, List<String> chosen)

{

    // base case; nothing left to choose

    //validate whether the elements are empty

    if (elements.isEmpty())

    {

        //display the chosen

        System.out.println(chosen);

    }

    else

    {

        //define the choice that is for first element

        String first = elements.remove(0);

        // two explorations: one with this first element, one without

        //add the first element

        chosen.add(first);

        //call the explore method

        explore(elements, chosen);

        //remove the element

        chosen.remove(chosen.size() - 1);

        //call the method

        explore(elements, chosen);

        // backtrack! 1st element is put back

        elements...