Description

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 11. 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. For example, do not add throws to the method headers since they are not necessary.
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 ArrayList 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 are expected to implement all of the methods in this homework. Each unimplemented method will result in a deduction.
8. You must submit your source code, the .java files, not the compiled .class files.
9. Only the last submission will be graded. Make sure your last submission has all required files. Resubmitting will void all previous submissions.
10. 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.
Style and Formatting
Javadocs
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 LinkedList<Integer>() instead of new LinkedList(). Using the raw type of the class will result in a penalty.
Forbidden Statements
• 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.
JUnits
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.
Binary Search Tree
You are to code a binary search tree, BST, which is a collection of nodes, each having a data item and a reference pointing to a left and a right child nodes. The BST must follow the order property: for any given node, its left child’s data and all of its children’s data must be less than the current node while its right child’s data and all of its children’s data must be greater than the current node. In order to compare the data, all elements added to the tree must implement Java’s generic Comparable interface.
It 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.
Recursion
Since trees are naturally recursive structures, all methods that are not O(1) must be implemented recursively, except for level order traversal. You’ll also notice that a lot of the public method stubs we’ve provided do not contain the parameters necessary for recursion to work, so these public methods act as “wrapper methods” for the user to use. You will have to write private recursive helper methods and call them in these wrapper methods. All of these helper methods must be private. To reiterate, do not change the method headers for the provided 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. It is not required, but it will make the homework cleaner, and it’ll also help greatly when we get to a later homework.
Nodes
The binary search tree consists of nodes. A class BSTNode is provided to you. BSTNode has getter and setter methods to access and mutate the structure of the nodes.
Methods
You will implement all standard methods for a Java data structure (add, remove, etc.) in addition to a few other methods (such as traversals). You must follow the requirements stated in the javadocs of each method you implement.
Traversals
Height
You will implement a method to calculate the height of the tree. The height of the tree is defined as the height of its root. The height of any given node is max(left node’s height, right node’s height) + 1. When doing this calculation, a leaf node has a height of 0 and a null node has a height of -1.
Comparable
As stated, the data in the BST must implement the Comparable interface. As you’ll see in the files, the generic typing of the BST and BSTNode classes will enforce this Comparable data requirement. You use the interface by making a method call like data1.compareTo(data2). This will return an int, and the value tells you how data1 and data2 are in relation to each other
• If the int is positive, then data1 is larger than data2.
• If the int is negative, then data1 is smaller than data2.
• If the int is zero, then data1 equals data2.
Note that the returned value can be any integer in Java’s int range, not just -1, 0, 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:
constructor 4pts
add 14pts
remove 20pts
get 5pts
contains 5pts
preorder 3pts
inorder 3pts
postorder 3pts
levelorder 3pts
height 3pts
clear 2pts
findPathBetween 10pts
Other:
Checkstyle 10pts
Efficiency 15pts
Total: 100pts
Provided
The following file(s) have been provided to you. There are several, but we’ve noted the ones to edit.
1. BST.java
This is the class in which you will implement the BST. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
2. BSTNode.java
This class represents a single node in the tree. It encapsulates the data, and the left and right references. Do not alter this file.
3. BSTStudentTest.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.
Deliverables
You must submit all of the following file(s) to the course Gradescope. Make sure all file(s) listed below are in each submission, as only the last submission will be graded. Make sure the filename(s) matches the filename(s) below, and that only the following file(s) are present. Do NOT submit BSTNode.java for this homework; if you do, your homework will not compile on Gradescope. If you resubmit, be sure only one copy of each file is present in the submission. If there are multiple files, do not zip up the files before submitting; submit them all as separate files.
Once submitted, double check that it has uploaded properly on Gradescope. To do this, download your uploaded file(s) to a new folder, copy over the support file(s), recompile, and run. It is your sole responsibility to re-test your submission and discover editing oddities, upload issues, etc.
1. BST.java