Homework 4: Binary Search Trees Solution





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 les 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 sig-natures.
  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 e ciency. Even if your method is to be O(n), traversing the structure multiple times is considered ine cient unless that is absolutely required (and that case is extremely rare).
  7. You must submit your source code, the .java les, not the compiled .class
  8. After you submit your les, redownload them and run them to make sure they are what you intended to submit. You are responsible if you submit the wrong les.

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 (you may also use iteration for one speci c edge case in remove(), see Javadoc for details). 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 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. 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 interface.


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.


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.

add 19pts
remove 20pts
get 5pts
contains 5pts
traversals 8pts
distanceBetween 8pts
height 3pts
clear 2pts
constructor 5pts
Checkstyle 10pts
E  ciency 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 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 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 Raymond Ortiz (rortiz9@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 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:

Bad: throw new IndexOutOfBoundsException(“Index is out of bounds.”);

Good: 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<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()


Arrays class Array class

Collections class


Re ection APIs

Inner or nested classes Lambda Expressions Method References

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.


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

  1. 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 le.

  1. 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.

  1. java

This class represents a single node in the BST. It encapsulates the data, left, and right reference. Do not alter this le.

  1. 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.


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.

After submitting, be sure you receive the con rmation email from T-Square, and then download your uploaded les 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. java


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