Homework 2: Stacks and Queues Solution

Description

There are general homework guidelines you must always follow. If you fail to follow any of the following guidelines, you risk receiving a 0 for the entire assignment.

1. All submitted code must compile under JDK 8. This includes unused code, so don’t submit extra les that don’t compile. Any compile errors will result in a 0.

2. Do not include any package declarations in your classes.

3. Do not change any existing class headers, constructors, instance/global variables, or method sig-natures. For example, do not add throws to the method headers since they are not necessary.

4. Do not add additional public methods.

5. Do not use anything that would trivialize the assignment. (e.g. Don’t import/use java.util.ArrayList for an ArrayList assignment. Ask if you are unsure.)

6. Always be very conscious of e ciency. Even if your method is to be O(n), traversing the structure multiple times is considered ine cient unless that is absolutely required (and that case is extremely rare).

7. You must submit your source code, the .java les, not the compiled .class les.

8. Only the last submission will be graded. Make sure your last submission has all required les. Resubmitting will void all previous submissions.

9. After you submit your les, redownload them and run them to make sure they are what you intended to submit. You are responsible if you submit the wrong les.

Collaboration Policy

Every student is expected to read, understand and abide by the Georgia Tech Academic Honor Code.

When working on homework assignments, you may not directly copy code from any source (other than your own past submissions). You are welcome to collaborate with peers and consult external re-sources, but you must personally write all of the code you submit. You must list, at the top of each le in your submission, every student with whom you collaborated and every resource you consulted while completing the assignment.

You may not directly share any les containing assignment code with other students or post your code publicly online. If you wish to store your code online in a personal private repository, you can use Github Enterprise to do this for free.

The only code you may share is JUnit test code on a pinned post on the o cial course Piazza. Use JUnits from other students at your own risk; we do not endorse them. See each assignment’s PDF for more details. If you share JUnits, they must be shared on the site speci ed in the Piazza post, and not anywhere else (including a personal GitHub account).

Violators of the collaboration policy for this course will be turned into the O ce of Student Integrity.

Style and Formatting

It is important that your code is not only functional, but written clearly and with good programming style. Your code will be checked against a style checker. The style checker is provided to you, and is

Homework 2: Stacks and Queues Due: See Canvas

located on Canvas. It can be found under Files, along with instructions on how to use it. A point is deducted for every style error that occurs. If there is a discrepancy between what you wrote in accordance with good style and the style checker, then address your concerns with the Head TA.

Javadocs

Javadoc any helper methods you create in a style similar to the existing javadocs. Any javadocs you write must be useful and describe the contract, parameters, and return value of the method. Random or useless javadocs added only to appease checkstyle will lose points.

Vulgar/Obscene Language

Any submission that contains profanity, vulgar, or obscene language will receive an automatic zero on the assignment. This policy applies not only to comments/javadocs, but also things like variable names.

Exceptions

When throwing exceptions, you must include a message by passing in a String as a parameter. The message must be useful and tell the user what went wrong. \Error”, \BAD THING HAP-PENED”, and \fail” are not good messages. The name of the exception itself is not a good message. For example:

Bad: throw new IndexOutOfBoundsException(‘‘Index is out of bounds.’’);

Good: throw new IllegalArgumentException(‘‘Cannot insert null data into data structure.’’); In addition, you may not use try catch blocks to catch an exception unless you catching an exception you have explicitly thrown yourself with the throw new ExceptionName(‘‘Exception Message’’); syn-

tax (replacing ExceptionName and Exception Message with the actual exception name and message respectively).

Generics

If available, use the generic type of the class; do not use the raw type of the class. For example, use new LinkedList<Integer>() instead of new LinkedList(). Using the raw type of the class will result in a penalty.

Forbidden Statements

You may not use these in your code at any time in CS 1332.

• package

• System.arraycopy()

• clone()

• assert()

• Arrays class

• Array class

• Thread class

• Collections class

• Collection.toArray()

• Re ection APIs

Homework 2: Stacks and Queues Due: See Canvas

• Inner or nested classes

• Lambda Expressions

• Method References (using the :: operator to obtain a reference to a method)

If you’re not sure on whether you can use something, and it’s not mentioned here or anywhere else in the homework les, just ask.

Debug print statements are ne, but nothing should be printed when we run your code. We expect clean runs – printing to the console when we’re grading will result in a penalty. If you submit these, we will take o points.

JUnits

We have provided a very basic set of tests for your code. These tests do not guarantee the correctness of your code (by any measure), nor do they guarantee you any grade. You may additionally post your own set of tests for others to use on the Georgia Tech GitHub as a gist. Do NOT post your tests on the public GitHub. There will be a link to the Georgia Tech GitHub as well as a list of JUnits other students have posted on the class Piazza.

If you need help on running JUnits, there is a guide, available on Canvas under Files, to help you run JUnits on the command line or in IntelliJ.

Homework 2: Stacks and Queues Due: See Canvas

Stacks and Queues

You are to code the following:

1. A Stack backed by a singly-linked list without a tail reference.

2. A Stack backed by an array

3. A Queue backed by a singly-linked list with a tail reference

4. A Queue backed by an array

A Stack is a last-in, rst-out (LIFO) data structure; the last item to be inserted is the rst item to be removed. A Queue is a rst-in, rst-out (FIFO) data structure; the rst item inserted is the rst item to be removed.

All your data structures must follow the requirements stated in the javadocs of each method you must implement.

Note that the linked versions of the data structures should NOT be circular.

Capacity

The starting capacity of the array classes should be the constant INITIAL CAPACITY de ned in the .java les. Reference the constant as-is. Do not simply copy the value of the constant. Do not change the constant. If, while adding an element, the array class does not have enough space, you should regrow the backing array to twice its old capacity. In other words, after one resize, the backing array’s length should be INITIAL CAPACITY * 2, and after two resizes, it should be INITIAL CAPACITY * 2 * 2. Do not resize the backing array when removing elements.

Removing

With both array classes, when elements are deleted from the array, the index the element was removed from should be set to null. All unused positions in the backing array must be set to null.

Circular Arrays

The backing array in your ArrayQueue implementation must behave circularly. This means the front variable might wraparound to the beginning when you remove to take advantage of empty space while maintaining O(1) e ciency for all operations.

For this assignment, the front variable in ArrayQueue should represent the index that holds the next element to dequeue. Failure to follow this convention will result in major loss of points.

For enqueuing, add to the back of the queue. To access the back of the queue, you can add the size to the front variable to get the next index to add to, though you will have to account for the circular behavior yourself. If there are empty spaces at the front of the array, the back of the queue should wrap around to the front of the array and make use of those spaces.

For dequeuing, you should simply treat the next index in the array as the new front. Do not shift any elements during a remove.

When resizing the backing array, \unwrap” the data. Realign the queue with the front of the new array during the transfer. The front variable of the queue is once again at index 0.

Homework 2: Stacks and Queues Due: See Canvas

Additionally, after removing the last element in the queue, move the front variable like you normally would. Do not explicitly reset it to 0. This e ectively means that going from size 1 to size 0 should not be a special case for your code.

The examples below demonstrate what the queue should look like at various states.

In the example below, the queue begins empty (initial state). An element is added.

In the example below, adding to the back causes the newly added element to wrap around to the front.

In the example below, adding another element causes the queue to resize. The array capacity is doubled and the front element moves to index 0.

In the example below, the last element of the queue is removed, but front moves as expected. The front variable is not explicitly set to 0.

Homework 2: Stacks and Queues Due: See Canvas

Grading

Here is the grading breakdown for the assignment. There are various deductions not listed that are incurred when breaking the rules listed in this PDF and in other various circumstances.

Methods:
ArrayStack constructor	1pts
ArrayStack push	7pts
ArrayStack pop	6pts
ArrayStack peek	4pts
LinkedStack push	6pts
LinkedStack pop	7pts
LinkedStack peek	4pts
ArrayQueue constructor	1pts
ArrayQueue enqueue	10pts
ArrayQueue dequeue	8pts
ArrayQueue peek	4pts
LinkedQueue enqueue	6pts
LinkedQueue dequeue	7pts
LinkedQueue peek	4pts
Other:
Checkstyle	10pts
E ciency	15pts
Total:	100pts

Provided

The following le(s) have been provided to you. There are several, but we’ve noted the ones to edit.

1. ArrayStack.java

This is the class in which you will implement the ArrayStack. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance vari-ables, or static variables.

2. LinkedStack.java

This is the class in which you will implement the LinkedStack. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance vari-ables, or static variables.

3. ArrayQueue.java

This is the class in which you will implement the ArrayQueue. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance vari-ables, or static variables.

4. LinkedQueue.java

This is the class in which you will implement the LinkedQueue. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance vari-ables, or static variables.

5. LinkedNode.java

Homework 2: Stacks and Queues Due: See Canvas

This class represents a single node in the linked list. It encapsulates the data and the next reference. Do not alter this le.

6. StackStudentTest.java

This is the test class that contains a set of tests covering the basic operations on the Stack classes. It is not intended to be exhaustive and does not guarantee any type of grade. Write your own tests to ensure you cover all edge cases.

6. QueueStudentTest.java

This is the test class that contains a set of tests covering the basic operations on the Queue classes. It is not intended to be exhaustive and does not guarantee any type of grade. Write your own tests to ensure you cover all edge cases.

Deliverables

You must submit all of the following le(s) to the course Gradescope. Make sure all le(s) listed below are in each submission, as only the last submission will be graded. Make sure the lename(s) matches the lename(s) below, and that only the following le(s) are present. Do NOT submit LinkedNode.java for this homework; if you do, your homework will not compile on Gradescope. If you resubmit, be sure only one copy of each le is present in the submission. If there are multiple les, do not zip up the les before submitting; submit them all as separate les.

Once submitted, double check that it has uploaded properly on Gradescope. To do this, download your uploaded le(s) to a new folder, copy over the support le(s), recompile, and run. It is your sole responsibility to re-test your submission and discover editing oddities, upload issues, etc.

1. ArrayStack.java

2. LinkedStack.java

3. ArrayQueue.java

4. LinkedQueue.java

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