Homework 5: AVL Solution

Description

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 5: AVL 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

Write javadocs 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 5: AVL 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 5: AVL Due: See Canvas

AVL

You are to code an AVL, which is a special type of binary search tree. It must follow the same rules as binary search trees: each node has 0-2 children, all data in the node’s left subtree is less than the parent node’s data, and all data in the node’s right subtree is greater than the parent node’s data. However, an AVL di ers from a BST with its self-balancing rotations, which you must implement.

All methods in the AVL that are not O(1) must be implemented completely recursively. This includes all helper methods. For methods that change the structure of the tree in some way, we highly recommend you use a technique taught in class called pointer reinforcement.

The AVL will have two constructors: a no-argument constructor (which should initialize an empty tree), and a constructor that takes in a collection of data to be added to the tree, and initializes the tree with this collection of data.

Balancing

Each node has two additional instance variables, height and balanceFactor. The height variable should represent the height of the node. If you recall, a node’s height is max(left node’s height, right node’s height) + 1 where the height of a null is -1. The balance factor of a node should be equal to its left child’s height minus its right child’s height. Since we’ve stored this information in each node, you no longer need to recursively compute it.

The tree should rotate appropriately to make sure it’s always balanced. A tree is balanced if every node’s balance factor is either -1, 0, or 1. Keep in mind that you will have to update the balancing information stored in the nodes on the way back up the tree after modifying the tree; the variables are not updated automatically.

Important Notes

Here are a few notes to keep in mind when switching from BST to AVL:

1. For two child remove, use the successor, not predecessor.

2. After every change to the tree, make sure to update height and balance factor elds of all nodes whose subtrees have been modi ed.

3. Make sure the height method is O(1).

Homework 5: AVL 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:
constructor	4pts
add	19pts
remove	24pts
get	5pts
contains	5pts
height	2pts
clear	2pts
predecessor	8pts
kSmallest	6pts
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. AVL.java

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

2. AVLNode.java

This class represents a single node in the tree. It encapsulates the data, the left and right references, the height, and the balanceFactor. Do not alter this le.

3. AVLStudentTest.java

This is the test class that contains a set of tests covering the basic operations on the AVL class. 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 AVLNode.java; 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.

Homework 5: AVL Due: See Canvas

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. AVL.java

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