CS1332 Homework 3 Solution

1. All submitted code must compile under JDK 11. This includes unused code, so don’t submit extra files 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 signatures. 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 efficiency. Even if your method is to be O(n), traversing the structure multiple times is considered inefficient unless that is absolutely required (and that case is extremely rare).
7. You are expected to implement all of the methods in this homework. Each unimplemented method will result in a deduction.
8. You must submit your source code, the .java files, not the compiled .class files.
9. Only the last submission will be graded. Make sure your last submission has all required files. Resubmitting will void all previous submissions.
10. After you submit your files, redownload them and run them to make sure they are what you intended to submit. You are responsible if you submit the wrong files.
Style and Formatting
Javadocs
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 HAPPENED”, 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.’’);
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
• package
• System.arraycopy()
• clone()
• assert()
• Arrays class
• Array class
• Thread class
• Collections class
• Collection.toArray()
• Reflection APIs
• 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 files, just ask.
Debug print statements are fine, 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 off points.
JUnits
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.
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, first-out (LIFO) data structure; the last item to be inserted is the first item to be removed. A Queue is a first-in, first-out (FIFO) data structure; the first item inserted is the first 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 defined in the .java files. 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. 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) efficiency 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.
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 effectively 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.

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
Efficiency 15pts
Total: 100pts
Provided
The following file(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 variables, 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 variables, 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 variables, 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 variables, or static variables.
5. LinkedNode.java
This class represents a single node in the linked list. It encapsulates the data and the next reference. Do not alter this file.
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.
7. 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 file(s). Make sure all file(s) listed below are in each submission, as only the last submission will be graded. Make sure the filename(s) matches the filename(s) below, and that only the following file(s) are present. If there are multiple files, do not zip up the files before submitting; submit them all as separate files.
Once submitted, double check that it has uploaded properly on Gradescope. To do this, download your uploaded file(s) to a new folder, copy over the support file(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