CS3901 Intermediate Programming and Data Structures Winter 2008 (Q2 AY 08) Assignment #5. Due: noon Tuesday, 3 March 2008

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1 CS3901 Intermediate Programming and Data Structures Winter 2008 (Q2 AY 08) Assignment #5 Due: noon Tuesday, 3 March 2008 Objective Practice with Java Create a CircularLinkedList implementation of List ADT Write a program based on the Josephus problem (see below) Review Class notes List ADT (Wu, Ch. 18) Preliminaries Flavius Josephus was a Jewish historian living in the 1st century. As his own account goes, he and his 40 comrade soldiers were trapped in a cave, surrounded by Romans. They chose suicide over capture and decided that they would draw lots to determine who would kill who. Josephus and one other man were the last remaining. Josephus convinced the other Jew that they should both surrender to the Romans rather than to kill themselves. Josephus attributed his survival to luck or to Providence, he knew not which. (From Wikipedia, Programming Exercise For this assignment, you re going to create a Java CircularLinkedList class. You ll test the class, then use it to write a program based on the Josephus problem. Step 0 Before starting, there is one more small bit of eclipse setup I d like you to do. Go to Preferences (under Window on Windows), and navigate to Java Code Style Code Templates Comments Overriding methods. (See the figure below.) 1

2 Click on Edit, and change the text exactly to the following: /** * ${tags */ The screen should look like the figure below. Click OK to close both dialog boxes. Step 1 For this assignment, you ll be creating your first eclipse java project. Right click in the package explorer and select New Java Project to create the <Your_last_name>_ CircularLinkedList project. Your last name should be capitalized. In the same way, select New Package to create a <your_last_name>_circularlinkedlist package inside the project (without capitalizing your last name). 2

3 Copy NPSList.java (on the web site) to this project (drag and drop from your desktop should work), and change the package of the file appropriately (eclipse can help with this). Next, create a new class in this package called NPSCircularLinkedList<E>. Next to interfaces, click Add, type NPSList, and press enter. Click on the newly created NPSList interface and manually add <E> at the end (see the figure below). Check all boxes for creating method stubs and comments. When everything looks exactly like the figure, click Finish. Step 2 Using NPSLinkedList from Chapter 18 of Wu as a guide, fill in NPSCircularLinkedList. Note that you will have to make small changes to most methods because you re working with a circularly linked list. It s your job to figure these out. Suggested steps: 1. Create an inner class ListNode, as in the book. An inner class is a small class included inside another class, and only usable within that other class. This should be put right above main(). 2. Add the necessary class data members (head, tail, count, NOT_FOUND). Optional. In a circularly linked list, you really only need a reference to the tail node; the list head can easily be located through tail.next. This makes some functions easier to implement. 3. Implement the constructor and clear() functions. 4. Implement the add(e item) function. 5. Add a public String tostring() method: public String tostring() { String retstr; ListNode ptr = head; retstr = "NPSCircularLinkedList\n"; 3

4 retstr += "Count: " + count + "\n"; retstr += "["; if (ptr!= null) { while (ptr!= tail) { retstr += "" + ptr.item + ", "; ptr = ptr.next; retstr += "" + ptr.item; retstr += "]"; return retstr; 6. Test out your class in main(), by creating a list, adding a few items, and printing it out. Here s an example: public static void main(string args[]) { NPSCircularLinkedList<Integer> myintlist = new NPSCircularLinkedList<Integer>(); myintlist.add(1); myintlist.add(2); myintlist.add(3); System.out.println(myIntList); System.out.println(); NPSCircularLinkedList<String> mystrlist = new NPSCircularLinkedList<String>(); mystrlist.add("item 1"); mystrlist.add("item 2"); mystrlist.add("item 3"); System.out.println(myStrList); This code should produce the following output: NPSCircularLinkedList Count: 3 [1, 2, 3] NPSCircularLinkedList Count: 3 [Item 1, Item 2, Item 3] 7. Implement and test the rest of the functions iteratively. Satisfactorily completing Step 2 will earn you a Check-minus on the assignment. Step 3 In this lab you are to simulate the Josephus problem. Your program will be written as a main() function in the file Josephus.java. The program command line contains an integer n representing the elimination order, followed by a list of names; for example, 4

5 $ java squire_circularlinkedlist.josephus 3 Andrea Peter Phil Michael Joanna Aaron Akshat Alexander Brandon Arthur (Note: you can add command line arguments within eclipse from the Run... dialog. Instead of choosing Run As Java Application, choose Run As Run..., and click on the Arguments tab.) The program should simulate the Josephus problem by repeatedly removing the nth name from the list and displaying it. At the end, display the name of the survivor. For the example above, your output should be: Phil is dead. Aaron is dead. Brandon is dead. Peter is dead. Akshat is dead. Andrea is dead. Alexander is dead. Joanna is dead. Arthur is dead. The survivor is Michael. It is possible to write this program with the existing methods in CircularLinkedList.java. However, you can write a nicer version which makes use of the circular link to simulate the circle of people. Add the following method: E removeandrotate(int index); removeandrotate() has the same semantics as remove(), with the following changes: 1. index may be any nonnegative integer. To remove the 37th element from a list of 10, just following the links 37 times and remove that element. (This is equivalent to removing the 7th element.) 2. After the removal, move the tail pointer so that it points to the element just prior to the one which was removed. If you haven t eliminated the head pointer, move it so that it points to the element just after the one which was removed. The effect of this is that in successive calls to remove(), each one resumes where the previous one finished. This is consistent with how a simulation of the Josephus problem should work. Your program for the Josephus problem should work by making successive calls to removeandrotate(). Satisfactorily completing Step 3 will earn you a Check-plus on the assignment. Extra Credit Implementing the steps below will earn you additional credit on the assignment. Create an interactive game, called JosephusGame.java. This program should 1. Read in a file with a list of names, one per line, to use during the game. Get the filename from the command line, then use something like this to read the file: Scanner scanner = new Scanner(new File(filename)); while ( scanner.hasnextline() ) { peoplecircle.add( scanner.nextline() ); scanner.close(); (See also Wu Section 12.3.) 2. Prompt a player for his/her name. 5

6 3. Choose a random number of people (5 n total number of people+1), and a random number to represent every which person to kill (2 n total number of people+1). (Alternately, prompt the player for these items). Tell the player how many people there are in the group and how they will be killed, and prompt him/her for where he/she would like to sit. Insert the player in the list at that position. 4. Run the Josephus simulation, as above, but stopping when the player is killed. Display an appropriate message, and ask the player if he/she would like to be resurrected to play again. Note that to play again, you should figure out a way to keep the list of players around so you don t have to read it in again. There are clever ways to accomplish this task. 5. Additional credit will be given for creating a nice GUI interface. (Wu, Ch 14). Talk to me if you would like to pursue this. See for a similar game. Submission 1. Read the Java Style guidelines. In particular, note that each file should have a title block at the top with // // Filename:.java <name of this file> // Name: <your name here> // Class: CS3901, Winter 2008 // Assignment #5: CircularLinkedList // Compiler: <JDK 6.0 etc> // All functions should have a javadoc above them (see the style guide), describing the function, all input parameters, any return value, and any exceptions thrown. All class member variables should also have a javadoc comment describing them, and various comments should be included in your program describing the functionality at various steps. 2. Complete a write-up with the following information: Homework Number Program Title Programmer Name Summary, including: (a) One paragraph describing the program status. Include what works, as well as a detailed description of what doesn t work (you maybe required to fix anything that doesn t work). (b) Something you learned. (c) A list of all help you received, including websites, books, and your classmates. Sample Output Save your writeup in the same directory as your programs, zip up the whole thing directory, and send it to me by by the due date. 6