Homework 4: BST Solution

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 the left and right child nodes. The BST must follow the order property: for any given node, its left child and all of its children must be less than the current node while its right child and all of its children 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: the 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.




You may import Java’s LinkedList/ArrayList classes for the 4 traversal methods and findPathBetween, but only for these methods.




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. These wrapper methods will just call another private helper method that is recursive. 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.










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Homework 4: BST Due: See Canvas










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




You will implement 4 di erent ways of traversing a tree: pre-order traversal, in-order traversal, post-order traversal, and level-order traversal. The rst 3 MUST be implemented recursively; level-order is best implemented iteratively. For a level-order traversal, you may use Java’s Queue interface (and an implementing class for it such as LinkedList).




Height




You will implement a method to calculate the height of the tree. The height of any given node is max(left node’s height, right node’s height) + 1. A leaf node has a height of 0. Based on this recursive de nition, this means that null nodes have a height of -1.




Comparable




As stated, the data in the BST must implement the Comparable interface. As you’ll see in the les, the generic typing has been speci ed to require that it implements the Comparable interface. 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 positive, then data1 data2. If negative, then data1 < data2. If 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.














































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Homework 4: BST
Due: See Canvas








Methods:














constructor
4pts












add
14pts












remove
20pts












get
5pts












contains
5pts












preorder
3pts












inorder
3pts












postorder
3pts












levelorder
3pts












height
3pts












clear
2pts












ndPathBetween
10pts












Other:














Checkstyle
10pts












E ciency
15pts












Total:
100pts















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.




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.





















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Homework 4: BST Due: See Canvas










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 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




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.




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.’’);




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()










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Homework 4: BST Due: See Canvas










Re ection 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 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.




Provided




The following le(s) have been provided to you. There are several, but we’ve noted the ones to edit.




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.




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 le.




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 le(s). Please make sure the lename(s) matches the lename(s) below, and that only the following le(s) are present. The only exception is that Canvas will automat-ically append a -n depending on the submission number to the le name. This is expected and will be handled by the TAs when grading as long as the le name before this add-on matches what is shown below. If you resubmit, be sure only one copy of the 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.




Once submitted, double check that it has uploaded properly on Canvas. To do this, download your uploaded les to a new folder, copy over the support les, recompile, and run. It is your sole responsi-bility to re-test your submission and discover editing oddities, upload issues, etc.




BST.java















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