# Homework 5: AVL Trees Solution

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## Description

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 di ers 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, except for level-order traversal. Good recursion with simple, focused states is strongly encouraged for this assignment in particular.

Your AVL tree will implement the AVL interface provided. 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 represents the height of the node (recall that a node’s height is max(child nodes’ heights)+1. The balance factor of a node is 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.

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.

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 Homework 5: AVL Trees Due: See T-Square Methods: add 15pts remove 15pts get 7pts contains 7pts traversals 12pts threshold 7pts height 3pts clear 4pts constructor 5pts Other: Checkstyle 10pts E ciency 15pts Total: 100pts

Keep in mind that add functions are necessary to test other functions, so if an add doesn’t work, remove tests might fail as the items to be removed were not added correctly. Additionally, the size function is used many times throughout the tests, so if the size isn’t updated correctly or the method itself doesn’t work, 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 T-Square under Resources, 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 in T-Square, under Resources, along with instructions on how to use it. We will take o a point for every style error that occurs. If you feel like what you wrote is in accordance with good style but still sets o the style checker please email Grayson Bianco (gbianco6@gatech.edu) with the subject header of \CheckStyle XML”.

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.

Exceptions

When throwing exceptions, you must include a message by passing in a String as a parameter. The mes-sage 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:

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Homework 5: AVL Trees Due: See T-Square

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

You may not use these in your code at any time in CS 1332.

break may only be used in switch-case statements

continue package

System.arraycopy() clone()

assert()

Arrays class Array class

Collections class

Collection.toArray()

Re ection APIs

Inner, nested, or private classes

Debug print statements are ne, but nothing should be printed when we run them. We expect clean runs – printing to the console when we’re grading will result in a penalty. If you use these, we will take o points.

Provided

The following le(s) have been provided to you. There are several, but you will only edit one of them.

1. AVLInterface.java

This is the interface you will implement in AVL. All instructions for what the methods should do are in the javadocs. Do not alter this le.

1. AVL.java

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

1. AVLNode.java

This class represents a single node in the AVL tree. Do not alter this le.

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Homework 5: AVL Trees Due: See T-Square

1. 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 le(s). Please make sure the lename matches the lename(s) below, and that only the following le(s) are present. T-Square does not delete les from old uploads; you must do this manually. Failure to do so may result in a penalty.