Homework 1: Singly-Linked List and Recursion Solution



Singly-Linked List

You are to code a singly-linked list with a head and a tail reference. A linked list is a collection of nodes, each having a data item and a reference pointing to the next node. The next reference for the last node in this list must be null, as it is not circular. Do not use a phantom node to represent the start or end of your list. A phantom or sentinel node is a node that does not store data held by the list and is used solely to indicate the start or end of a linked list. If your list contains n elements, then it should contain exactly n nodes.

Your linked list implementation will implement the LinkedListInterface provided. It will use the default constructor (the one with no parameter) which is automatically provided by Java. Do not write your own constructor.


The linked list consists of nodes. A class SLLNode is provided to you. SLLNode has three methods to access and set the next node, and to access the data in the node.


You will implement three add() methods. One will add to the front, one will add to the back, and one will add anywhere in the list. When adding the rst element to an empty list, the new node should be both the head and the tail. See the interface for more details.


Removing, just like adding, can be done from the front, the back, or anywhere in your linked list. In addition, the rst instance of a speci c value from the list can be removed. When removing from the front, the rst node should be removed and the head reference should be updated. When removing from the back, the last node should be removed and the tail reference should be updated. When removing


Homework 1: Singly-Linked List and Recursion Due: See T-Square

from the middle, the previous node of the removed node should point to the next node of the removed node. Make sure that you set any pointers to the deleted nodes to null. See the interface for more details.

Comparaing Data

For the findLargestElement() method, you will need to compare the elements in your list to the given data. You may be tempted to use == like with primitives, but this does not work as expected with objects. In Java, using the == operator, < operator, > operator, <= operator, or >= operator are valid for comparing primitive types, but are not valid for comparing objects. Java will not allow you to use binary operators to compare objects. Therefore, the generic type for SinglyLinkedList implements the Comparable interface, and you can use the compareTo() method to compare two objects.


You are to code two methods whose solutions must be written recursively. Recursion is a means of breaking down a problem into a set of smaller sub-problems. This process of breaking down the problem ends when we reach a “base case”, a condition to which a problem is at its most basic form and can be solved without recursion. In regards to functions, recursion is when a function calls itself but in a modi ed and simpler state. The calls will eventually converge to the base case, in which the recursive call will return through the previous calls, utilizing the solution of current call as part of the solution to the caller. Your solution must be in what is considered “proper format”: a base case check followed by logic that will reduce the recursion toward the base case.



if (x == 0) {

print “We reached the base case!”

} else {

print “Let’s get closer”



Private recursive helper methods

Note that you must utilize a private helper method to execute the logic of your recursion. The main reason for this is that it adds a layer of abstraction between the main method and the recursive logic. In most cases, the recursion requires the use of more parameters than the main call has in its method signature. Therefore, we will make a private method that has the additional parameters that we need. Both methods in Recursion.java must have private helper methods. All private helper methods, as per Checkstyle requirements, must have proper Javadocs.


A palindrome is a sequence of characters such that it can be read forwards and backwards with the same resulting test. An example of a palindrome is “A nut for a jar of tuna”. Logically, we can see that if we remove the ’a’ at the front and at the back, the remaining text is still a palindrome. This leads us to the recursive de nition of a palindrome is another palindrome with a character appended to the front and the same character appended to the back. We will consider a sequence of one or zero characters being a palindrome.


Homework 1: Singly-Linked List and Recursion Due: See T-Square

Greatest Common Divisor (GCD)

The greatest common divisor is the largest number that can divide two or more numbers evenly. Euclid’s algorithm is a recursive solution to calculate the GCD of two numbers. More details about GCD are provided in the Javadocs in the Recursion.java le.


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.































E ciency




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 SinglyLinkedList.java and Recursion.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 (when it comes up).

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”.


Homework 1: Singly-Linked List and Recursion Due: See T-Square


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:

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 ArrayList<Integer>() instead of new ArrayList(). 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

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.


Homework 1: Singly-Linked List and Recursion Due: See T-Square


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

  1. LinkedListInterface.java

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

  1. SinglyLinkedList.java

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

  1. SLLNode.java

This class represents a single node in the linked list. It encapsulates data and the next reference. Do not alter this le.

  1. SinglyLinkedListStudentTests.java

This is the test class that contains a set of tests covering the basic operations on the SinglyLinkedList 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.

  1. Recursion.java

This is a class in which you will implement the recursive method solutions.All instructions for what the methods should do are in the javadocs.

  1. RecursionStudentTests.java

This is the test class that contains a set of tests covering the basic operations on the Recursion 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. 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. SinglyLinkedList.java

  1. Recursion.java


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