CS 112 - Introduction to Computer Science II Homework #6

Due: At the beginning of class 18.

NOTE: This work is to be done in pairs.  I strongly recommend the practice of Pair Programming described simply here.  Although team members are permitted to divide work, each team member should be able to informally present all work of his/her teammate.

The first two exercises will be based on the Java generics MyLinkedList code we will develop in class.  The test code we create for MyLinkedList can be easily adapted to test your exercise work.

NOTE: Do not use class MyLinkedListNode directly when implementing the classes of the assignment.  Only your MyLinkedList class will refer to MyLinkedListNode.  Do not use anything beyond the public methods of MyLinkedList that we defined together.

• You don't need it, and you'll get a compilation error on submission if you try to use a MyLinkedListNode or any field referring to one (e.g. MyLinkedList private fields head and tail). 
• MyStack and MyQueue can (and should) be implemented entirely by creating a MyLinkedList object as a private field and then calling the appropriate methods (not fields) on that object.
• Your code will be tested with my own MyLinkedList.java implementation (not yours) which allows no access to MyLinkedListNodes whatsoever, so your code will not compile during testing if you make use of MyLinkedList features beyond our public methods.

1. MyStack: Implement MyStack.java according to this specification.

2. MyQueue: Implement MyQueue.java according to this specification.

3. MahFravrit: Implement MahFravrit.java according to this specification.  This class essentially allows a generic set of items to be collected and returns a favorite ("fravrit") item from the set much like a priority queue, but with a difference: You'll implement this without relying on an efficient priority queue implementation.  Your efficiency requirement is to ensure that a favorite item is found in time linearly proportional to the number of items. 

Notes:

• Remember that your constructor's Comparator parameter will simply be lost if one doesn't store it in a more persistent type of variable.  What does this imply for your MahFravrit design?
• We don't know how many items the object will contain, so what simple data structure can help you hold an unknown number of items?  Have one as a field of your object.
• You don't need to know how to define a Comparator object for this assignment.  What you do need to figure out is how to use a Comparator to compare two items so that you can go through your items and determine the "fravrit", i.e. which item is "greater" in the order according to the given Comparator.  A Comparator is a standard Java class, so for this task, you need to look it up in the "Java SE API Documentation " linked to from our home page. (You can also find tutorials online. Note the similarity of Comparator to the Comparable interface of Section 13.6. This comparison is made in our text in Section 20.6.)

An explanation of the meme this assignment draws its strange vocabulary from may be found by clicking on the image below or watching this erudite video explanation.

Ermahgerd! Here is some test code to illustrate the use of MahFravrit class!

	public static void main(String[] args) {
		// In this first example, we use random integers and prefer larger integers as fravrits (favorites).
		int size = 20;
		MahFravrit<Integer> intFravrit = new MahFravrit<Integer>(new Comparator<Integer>() 
		{
			public int compare(Integer v1, Integer v2) {
				return v1 - v2;
			}
		});
		// Add random integers, possibly with repetition.
		for (int i = 0; i < size; i++) {
			int item = (int) (size * Math.random());
			System.out.print(item + " ");
			intFravrit.add(item);
		}
		System.out.println();
		// Successively, remove integers, greatest to least as we've defined our preference with the Comparator above.
		for (int i = 0; i < size; i++) 
			System.out.print(intFravrit.getFravrit() + " ");
		System.out.println();

		// In this next example, we use Strings with book names and prefer later Strings lexicographically, 
		// except for "Gersberms", which are MOST preferred because "ERMAHGERD! GERSBERMS ... MAH FRAVRIT BERKS!" 
		// http://knowyourmeme.com/memes/ermahgerd
		MahFravrit<String> berkFravrit = new MahFravrit<String>(new Comparator<String>() 
		{
			public int compare(String v1, String v2) {
				if (v1.equals("Gersberms"))
					return 1;
				else if (v2.equals("Gersberms"))
					return -1;
				else
					return v1.compareTo(v2);
			}
		});
		berkFravrit.add("The Hobbit");
		berkFravrit.add("Gersberms");
		berkFravrit.add("Diary of a Wimpy Kid");
		System.out.println(berkFravrit.getFravrit());
		System.out.println(berkFravrit.getFravrit());
		System.out.println(berkFravrit.getFravrit());
	}

Sample output:

12 11 1 4 18 11 13 0 2 2 6 2 1 11 3 8 1 16 8 15 
18 16 15 13 12 11 11 11 8 8 6 4 3 2 2 2 1 1 1 0 
Gersberms
The Hobbit
Diary of a Wimpy Kid

Your random integers will be different but ordered high to low in the second line.

Rubric: (20 points total)

• 6 points: MyStack
• 6 points: MyQueue
• 8 points: MahFravrit