Homework 7: AVL Trees 

Homework 7: AVL Trees 
Important
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
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.
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 Array List 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 must submit your source code, the .java files, not the compiled .class files.
8. 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.
AVL
You are required to implement an AVL tree. An AVL is a special type of binary search tree that follows
all the same rules: each node has 0-2 children, all data in the left subtree is less than the node’s data,
and all data in the right subtree is greater than the node’s data. The AVL differs from the BST with its
own self-balancing rotations, which you must implement.
All methods in the AVL tree that are not O(1) must be implemented recursively. Good recursion with simple, focused states is strongly encouraged for this assignment in particular.
It will have two constructors: a no-argument constructor (which should initialize an empty tree), and a
constructor that takes in data to be added to the tree, and initializes the tree with this data.
Balancing
Each node has two additional instance variables, height and balanceFactor. The height variable
should represent the height of the node (recall that a node’s height is max(child nodes’ heights) +
1. The balance factor of a node should be equal to its left child’s height minus its right child’s height.
The tree should rotate appropriately to make sure it’s always balanced. Keep in mind that you will have
to update these instance variables 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 trees:
1. Use the predecessor, not successor.
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Homework 7: AVL Trees Due: See Canvas
2. After every change to the tree, make sure to update height and balance factor fields of all nodes
whose subtrees have been modified.
3. Make sure the height method is O(1).
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:
add 19pts
remove 25pts
get 5pts
contains 5pts
maxDeepestNode 7pts
deepestCommonAncestor 7pts
clear 2pts
height 2pts
constructor 3pts
Other:
Checkstyle 10pts
Efficiency 15pts
Total: 100pts
Keep in mind that some functions are dependent on others to work, such as remove methods requiring
the add methods to work. Also, the size function is used many times throughout the tests, so if the size
isn’t updated correctly, many tests can fail.
A note on JUnits
We have provided a very basic set of tests for your code, in AVLStudentTests.java. These tests do
not guarantee the correctness of your code (by any measure), nor does it 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.
Style and Formatting
It is important that your code is not only functional but is also written clearly and with good style. We
will be checking your code against a style checker that we are providing. It is located on Canvas, under
Files, along with instructions on how to use it. We will take off a point for every style error that occurs.
If you feel like what you wrote is in accordance with good style but still sets off the style checker please
email Tim Aveni (tja@gatech.edu) with the subject header of “[CS 1332] CheckStyle XML”.
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.
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Homework 7: AVL Trees Due: See Canvas
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
LinkedNode<Integer() instead of new LinkedNode(). 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()
• 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.
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Homework 7: AVL Trees Due: See Canvas
Provided
The following file(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 AVL. It encapsulates the data, height, balanceFactor,
and left and right references. Do not alter this file.
3. AVLStudentTests.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 file(s). Please make sure the filename matches the filename(s)
below, and that only the following file(s) are present. If you make resubmit, make sure only one copy of
the file is present in the submission.
After submitting, double check to make sure it has been submitted on Canvas and then download your
uploaded files to a new folder, copy over the support files, recompile, and run. It is your responsibility
to re-test your submission and discover editing oddities, upload issues, etc.
1. AVL.java
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