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.
Deque
Stack and Queue are LIFO (last in, first out) and FIFO (first in, first out) data structures respectively. A Stack requires you to add and remove from the same end of the data structure, while a Queue requires you to add and remove from opposite ends of the data structure.
For this assignment, you are to code two implementations of a Deque, which is short for “double-ended queue.” A Deque allows for efficient adding and removing from both ends of the data structure.
The first implementation is backed by a circular array, and the second implementation is backed by a non-circular doubly-linked list.
ArrayDeque
The backing array in your ArrayDeque implementation must behave circularly. This means your front variable should wraparound to the beginning and end of the array as you add and remove to take advantage of empty space while maintaining O(1) efficiency for all operations. Near the bottom of the ArrayDeque.java file, there is a helper method called mod(int index, int modulo) to help you with the math part of this circular logic. This mod function is similar to the normal mod operator (%), but handles negative numbers as a circular array would expect (if the regular mod returns a negative, adds the result by the divisor).
The starting capacity of the ArrayDeque should be the constant INITIAL CAPACITY defined in ArrayDeque.java. 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 ArrayDeque does not have enough space, you should regrow the backing array to twice its old capacity. Do not regrow the backing array when removing elements.
Your front variable in ArrayDeque should represent the index holding the first element of the deque. Failure to follow this convention will result in major loss of points.
When regrowing the backing array, “unwrap” the data. Realign the deque with the front of the new array during the transfer. The front variable of the deque is once again at index 0.
Do not shift any elements during a remove. This also means that if there are empty spaces at the front of the array when adding, the back of the deque should wrap around to the front of the array and make use of those spaces.
Additionally, after removing the last element in the deque, 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 deque should look like at various states.
In the example below, the deque begins empty (initial state). When adding to the front, the front wraps around to the back. The element ends up at the end of the array, since adding to the front adds to the index before the front variable.

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 deque to resize. The array capacity is doubled and the front element moves to index 0.

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

LinkedDeque
In order to efficiently add/remove from both the front and back of a linked list in O(1) time, we need a doubly-linked list with a head and tail pointer. Your linked implementation will be backed by a doublylinked list. The LinkedDeque must follow the requirements stated in the javadocs of each method you must implement.
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:
ArrayDeque addFirst 9pts
ArrayDeque addLast 9pts
ArrayDeque removeFirst 8pts
ArrayDeque removeLast 8pts
ArrayDeque getFirst 4pts
ArrayDeque getLast 4pts
LinkedDeque addFirst 6pts
LinkedDeque addLast 6pts
LinkedDeque removeFirst 7pts
LinkedDeque removeLast 7pts
LinkedDeque getFirst 4pts
LinkedDeque getLast 3pts
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. ArrayDeque.java
This is the class in which you will implement the ArrayDeque. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
2. LinkedDeque.java
This is the class in which you will implement the LinkedDeque. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
3. LinkedNode.java
This class represents a single node in the linked list. It encapsulates the data, and the previous and next references. Do not alter this file.
4. DequeStudentTest.java
This is the test class that contains a set of tests covering the basic operations on the ArrayDeque and LinkedDeque 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) to the course Gradescope. 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. 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 file is present in the submission. 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. ArrayDeque.java
2. LinkedDeque.java