Homework 3: Deque Solution

Deque




Stack and Queue are LIFO and FIFO 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 e cient adding and removing from both ends of the data structure.




The rst 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) e ciency for all operations. Near the bottom of the ArrayDeque.java le, 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 de ned 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 rst element of the deque.







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Homework 3: Deque Due: See Canvas










Failure to follow this convention will result in major loss of points.




To access the back of the queue, you can add the size to the front variable to get the index of the back of the deque, though you will have to account for the circular behavior yourself.




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, 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 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 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







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variable is not explicitly set to 0.











































LinkedDeque




In order to e ciently 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 doubly-linked 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




E ciency
15pts




Total:
100pts







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.










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Homework 3: Deque Due: See Canvas










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 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. If a method is overridden or implemented from a superclass or an interface, you may use @Override instead of writing 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.’’);




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







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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




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.




Provided




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




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 vari-ables, or static variables.




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 vari-ables, or static variables.
















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Homework 3: Deque Due: See Canvas










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 le.




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 le(s). Please make sure the lename(s) matches the lename(s) below, and that only the following le(s) are present. The only exception is that Canvas will automat-ically append a -n depending on the submission number to the le name. This is expected and will be handled by the TAs when grading as long as the le name before this add-on matches what is shown below. If you resubmit, be sure only one copy of the 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 Canvas. To do this, download your uploaded les to a new folder, copy over the support les, recompile, and run. It is your sole responsi-bility to re-test your submission and discover editing oddities, upload issues, etc.




ArrayDeque.java



LinkedDeque.java



































































































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