CS 1332 Homework 4: Binary Search Trees




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Binary Search Tree
You are to code a binary search tree. A binary search tree is a collection of nodes, each having a data
item and a reference pointing to the left and right child nodes. The left child node and all of its children
are less than the data. The right child node and all of its children are greater than the data. Therefore,
all elements added to the tree must implement Java’s generic Comparable interface.
All methods in the BST that are not O(1) must be implemented recursively, except for level
order traversal.
Your binary search tree implementation will implement the BST interface provided. It will have two
constructors: the 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. Any attempts to add
data that is already in the tree should be ignored (the tree shouldn’t be changed, and the duplicate item
shouldn’t get added).
The binary search tree consists of nodes. The BSTNode class will be given to you; do not modify it.
You will implement all standard methods for a Java data structure (add, remove, etc.). See the interface
for details. Note that some methods are worth more than others. If add is incorrect, then you are likely
to fail most tests, as adding is crucial to the usability of a data structure.
You will implement 4 different ways of traversing a tree: pre-order traversal, in-order traversal, postorder traversal, and level-order traversal. The first 3 MUST be implemented recursively; level-order is
Homework 4: Binary Search Trees Due: See T-Square
best implemented iteratively. You may import Java’s LinkedList/ArrayList classes as appropriate for
these methods (but they may only be used for these methods). For a level-order traversal, you may use
Java’s Queue class.
You will implement a method to calculate the height of the tree. The height of any given node is
max(left.height, right.height) + 1. A leaf node has a height of 0.
A note on JUnits
We have provided a very basic set of tests for your code, in BSTStudentTests.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 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 Carey MacDonald (careyjmac@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. 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.
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:
throw new PDFReadException(“Did not read PDF, will lose points.”);
throw new IllegalArgumentException(“Cannot insert null data into data structure.”);
If available, use the generic type of the class; do not use the raw type of the class. For example, use new
LinkedList() instead of new LinkedList(). Using the raw type of the class will result in a
Homework 4: Binary Search Trees Due: See T-Square
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()
• Reflection APIs
• Inner or nested classes
Debug print statements are fine, 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
off points.
The following file(s) have been provided to you. There are several, but you will only edit one of them.
1. BSTInterface.java
This is the interface you will implement in BST. All instructions for what the methods should do
are in the javadocs. Do not alter this file.
2. BST.java
This is the class in which you will implement BSTInterface. Feel free to add private helper methods
but do not add any new public methods, inner/nested classes, instance variables, or
static variables.
3. BSTNode.java
This class represents a single node in the BST. It encapsulates the data, left, and right reference.
Do not alter this file.
4. BSTStudentTests.java
This is the test class that contains a set of tests covering the basic operations on the BST 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.
Homework 4: Binary Search Trees Due: See T-Square
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. T-Square does not delete files from old uploads;
you must do this manually. Failure to do so may result in a penalty.
After submitting, be sure you receive the confirmation email from T-Square, and then download your
uploaded files to a new folder, copy over the interfaces, recompile, and run. It is your responsibility to
re-test your submission and discover editing oddities, upload issues, etc.
1. BST.java