Chapter 12, Problem 22E

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...