COMP 250 Winter 2023 Assignment 2
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Assignment 2
COMP 250
Winter 2023
posted: Friday, March 3, 2023
due: Monday, March 20, 2023 at 11:59m
Learning Objectives
This assignment is meant for you to practice different data structures and their applications. A lot of the design decisions have been done for you, but you might notice that the instructions for A2 are less complete than A1. You will need to take care of small details by yourself. Finally, we will not be grading your work on efficiency; however, if a method takes more than 1 second to complete, it is equivalent to failing.
General Instructions
This assignment contains 3 parts. You need to download the files provided and complete the following 13 files:
Part I |
Part II |
Part III |
MyList.java MyLinkedList.java MyDoublyLinkedList.java MyStack.java MyQueue java |
Position.java TargetQueue.java Direction.java ActionQueue.java |
Region.java Caterpillar.java State.java World.java |
• Except for the MyDoublyLinkedList .java, where a starting file is provided, you have to create all the above classes from scratch.
• Please make sure that all the files you submit are part of a package called assignment2.
• You are NOT allowed to import any other class/interface except NoSuchElementException and Iterator, which have already been imported for you in MyDoublyLinkedList .java. You are also not allowed to use ANY field of type array. Any failure to comply with these rules will give you an automatic 0.
• You are always allowed to add private methods/fields whenever you think this can improve your implementation. You are also allowed to override the toString method if this can help you during the debugging process.
• Two extra files, CaterpillarGame .java and CaterpillarDrawer .java, are provided for vi- sualizing the results of Part III. Do not use them unless your Part III is completed and passes all tests from the minitester.
• Do NOT start testing your code only after you are done writing the entire assignment. It will be extremely hard to debug your program otherwise. If you need help debugging, feel free to reach out to the teaching staff. When doing so, make sure to mention what is the bug you are trying to fix, what have you tried to do to fix it, and where have you isolated the error to be.
Submission instructions
• Late assignments will be accepted up to 2 days late and will be penalized by 10 points per late day. Note that submitting one minute late is the same as submitting 23 hours late. We will deduct points for any student who has to resubmit after the due date (i.e. late) irrespective of the reason, be it the wrong file submitted, the wrong file format submitted or any other reason. We will not accept any submission after the 2 days grace period.
• Don’t worry if you realize that you made a mistake after you submitted: you can submit multiple times but only the latest submission will be evaluated. We encourage you to submit a first version a few days before the deadline (computer crashes do happen and Ed Lessons may be overloaded during rush hours).
• Do not submit any other files, especially .class files and the tester files. Any failure to comply with these rules will give you an automatic 0.
• Whenever you submit your files to Ed, you will see the results of some exposed tests. If you do not see the results, your assignment is not submitted correctly. If your assignment is not submitted correctly, you will get an automatic 0. If your submission does not compile on ED, you will get an automatic 0.
• The assignment shall be graded automatically on ED. Requests to evaluate the assign- ment manually shall not be entertained, and it might result in your final marks being lower than the results from the auto-tests. Please make sure that you follow the instruction closely or your code may fail to pass the automatic tests.
• The exposed tests on ED are a mini version of the tests we will be using to grade your work. If your code fails those tests, it means that there is a mistake somewhere. Even if your code passes those tests, it may still contain some errors. Please note that these tests are only a subset of what we will be running on your submissions, we will test your code on a more challenging set of examples. Passing the exposed tests assures you that your submission will not receive a grade lower than 40/100. We highly encourage you to test your code thoroughly before submitting your final version.
• Next week, a mini-tester will also be posted. The mini-tester contains tests that are equivalent to those exposed on Ed. We encourage you to modify and expand it. You are welcome to share your tester code with other students on Ed. Try to identify tricky cases. Do not hand in your tester code.
• Failure to comply with any of these rules will be penalized. If anything is unclear, it is up to you to clarify it by asking either directly a TA during office hours, or on the discussion board on Ed.
PART - I: Data Structures (35 points)
For the first part, you will write several classes to implement different data structures.
[5 points] Write an interface MyList
face extends the Iterable
• A getSize method that returns an int indicating the number of elements in the list.
• A isEmpty method that returns a boolean indicating whether the list is empty.
• An add method that appends the specified element to the end of this list and does not return anything.
• A clear method that removes all of the elements from this list and does not return anything.
• A remove method that removes the last element from the list and returns it.
[5 points] Write an abstract class MyLinkedList
The MyLinkedList
• A int indicating the size of the list.
The class must also implement the public methods getSize and isEmpty as specified by the documentation of the interface MyList
[15 points] Complete the MyDoublyLinkedList
generic type E. Inside the file provided you can find:
• A private class called DLLIterator and a method iterator returning a DLLIterator ob-
ject. This DLLIterator class implements the Iterator
• A private class called DNode. The DNode class contains three private fields:
– An E named element indicating the element stored in the node
– A DNode named next indicating the next node in the list
– A DNode named prev indicating the previous node in the list
• The MyDoublyLinkedList
– A DNode named head indicating the head of the list
– A DNode named tail indicating the tail of the list
It is up to you to do the following:
• Make sure the class MyDoublyLinkedList
• Implement the public methods add, remove, and clear as specified in the documenta- tion of the interface MyList
• Add the following public methods to the MyDoublyLinkedList
– An addFirst and an addLast method which takes input as an object of the generic type E and adds the element as the first/last element of the list. These methods do not return anything.
– A removeFirst and a removeLast method which removes the first/last node from the list and returns the element. The method should throw a NoSuchElementException if the list is empty.
– A peekFirst and a peekLast method which returns the first/last element without removing it from the list. The method should throw a NoSuchElementException if the list is empty.
– An equals method that takes an Object as an input; the method returns true if all elements in the list are considered to be equal and false otherwise.
You are free to add any additional private methods and/or fields to either MyDoublyLinkedList
[5 points] Write a class MyStack
The MyStack
• A MyDoublyLinkedList
The class must also have the following public methods:
• A constructor that takes no inputs and creates an empty stack.
• A push method that takes an input of type E and adds the input to the top of the stack.
• A pop method that removes the top of the stack and returns it. The method should throw a NoSuchElementException if the stack is empty.
• A peek method that returns the element at the top of the stack without removing it. The method should throw a NoSuchElementException if the stack is empty.
• A isEmpty method that returns true if the stack is empty and false otherwise.
• A clear method that clears the stack (i.e. removes all the elements from the stack).
• A getSize method that returns the number of elements in the stack.
[5 points] Write a class MyQueue
The MyQueue
• A MyDoublyLinkedList
The class must also have the following public methods:
• A constructor that takes no inputs and creates an empty queue.
• A enqueue method that takes an input of type E and adds it to the back of the queue.
• A dequeue method that removes the first element from the front of the queue and returns it. The method should throw a NoSuchElementException if the queue is empty.
• An isEmpty method that returns true if the queue is empty and false otherwise.
• A clear method that clears the queue (i.e. removes all the elements from the queue).
• An equals method that takes as input an Object and returns true if the input is another queue with equal elements, and false otherwise.
PART - II: Information Parsing with Stacks (35 points)
In PART-II, you will decode and parse strings that contain compressed information.
[7 points] Write a Position class as a representation of a point (x,y) on a 2D map as the figure below. The origin (0,0) is located at the top-left corner of the map.
(0,0) |
(1,0) |
(2,0) |
→ |
(0,1) |
(1,1) |
(2,1) |
|
(0,2) |
(1,2) |
(2,2) |
|
|
|
|
|
The Position class has the following private fields:
• An int indicating the x-coordinate on the map
• An int indicating the y-coordinate on the map
The Position class must also have the following public methods:
• A constructor that takes two int as inputs indicating the x- and y-coordinates on a map, in this order. The constructor uses the inputs to initialize the corresponding fields.
• A constructor that takes a Position as input and initializes the fields with the corre- sponding input. This type of constructors are called copy constructors. They are used to create duplicates of existing instances of the class.
• A reset method that takes two int as inputs indicating the x- and y-coordinates on a map. The method uses the inputs to resets the corresponding fields.
• A reset method that takes Position as input and resets the corresponding fields using the values of those of the input object.
• A static method called getDistance that takes two Position objects as input and returns the absolute distance between them in terms of the x- and y- coordinates. For example, the distance between two Position objects (2,3) and (3,5) is 3 (i.e. |2-3| + |3-5|).
• A getX and a getY method that return the values of the corresponding fields.
• A moveWest method that decrements the x-coordinate by 1.
• A moveEast method that increments the x-coordinate by 1.
• A moveNorth method that decrements the y-coordinate by 1.
• A moveSouth method that increments the y-coordinate by 1.
• An equals method which takes as input an Object and returns true if the input matches this in type, x-coordinate, and y-coordinate. Otherwise, the method returns false.
[13 points] Write a TargetQueue class that extends from MyQueue
Figure 1: A queue of positions after parsing "(1,2) . (3,4) . (5,6)"
Note that, the input string has this strict format (x,y). The x- and y-coordinates are enclosed by a left and a right parenthesis separated by a comma, and two positions must be separated by a period.
The TargetQueue class has the following private fields:
• A MyStack
The TargetQueue class must also have the following public methods:
• A constructor that takes no input. The constructor should invoke the constructor of the superclass and initialize its fields.
• A clear method that clears this queue and its stack field.
• An addTargets method that takes input as a String and parses it into a queue of Positions. The method should throw an IllegalArgumentException if the syntax of the input is invalid. It can be useful for this method to have a local String variable to store the numbers contained in the input string. I will refer to this variable as num. To check the validity of the syntax and parse out the information regarding the positions, we need to iterate through every character in the input string.
– if the character is a left parenthesis, the stack and num should both be empty. If so, push "(" onto the stack.
– if the character is a digit, append the digit to num.
– if the character is a comma, check if num is a valid integer. If num is empty, we must have read a comma before the x-coordinate, which is a syntax error. Otherwise, push num and "," onto the stack, in exactly this order. Finally, reset num.
– if the character is a right parenthesis
* the stack should contain 3 elements with exactly the order a comma, an integer, and a left parenthesis from the top. If the order is not correct or any of the elements are missing, the input string has a syntax error.
* num should be an integer representing the y-coordinate. If num is empty, we must have reached the right parenthesis without finding a y-coordinate, which is a syntax error.
* If the syntax is correct, add the x-y coordinate as a Position object onto the queue and reset num.
– if the character is a period, we must have reached the end of expression for a par- ticular position. If the syntax is correct, the stack and num should both be empty. Otherwise, this is another syntax error.
Note that, these are the minimum cases of syntax errors that you should take care of. There might be more edge cases that do not get detected by the instructions above. It
would be your job to find them and throw exceptions when needed.
[2 points] Write an enumeration Direction.
An enumeration in java is a special data type that represents a fixed set of constants. Defining and using enumerations will make your code a bit more readable. The syntax is as follows:
Defining an Enumeration |
Using Enumeration |
public enum ENUM_NAME { LABEL_1, LABEL_2, ... LABEL_N } |
ENUM_NAME e = ENUM_NAME .LABEL_1 ; ENUM_NAME f = ENUM_NAME .LABEL_2 ; ... switch (e) { case LABEL_1: break ; case LABEL_2: break ; } |
Inside a file called Direction .java you should define an enumeration called Direction that represents the directions. The enumeration Direction has four values NORTH, SOUTH, WEST,
EAST.
[13 points] Write a ActionQueue class that extends MyQueue
K[D]
which indicates that the direction(s) D is repeated K times. K should be a positive number. D should contain characters ‘N’, ‘S’, ‘W’, ‘E’ that represent directions. Specifically, ‘N’ stands for NORTH, ‘S’ stands for SOUTH, ‘W’ stands for WEST, and ‘E’ stands for EAST. Table 1 contains some examples of encoded strings and their decoded values:
Note that, implementing this class is meant to be a bit more challenging, and hence, the implementation details are omitted. You will need to understand and analyze the task at hand and decide how to go about implementing such class.
Encoded |
Decoded |
3[N] 3[NE] 3[2[N]2[E]]1[S] 2E[N] EN] E[EN] A |
NNN NENENE NNEENNEENNEES Syntax Error: E before 2 Syntax Error: Missing [ Syntax Error: Missing K Syntax Error: Unknown Character A |
Table 1: Examples of encoded and decoded directions
It is up to you to decide how many, and what type of private fields you might need for this class. Different implementations are possible. Remeber to exploit the properties of stacks to help you parse strings.
The ActionQueue class must have the following public methods:
• A constructor that takes no input and takes care of initializing whichever field(s) you have added.
• A clear method that removes all items from this queue (and possibly clears the field(s))
• A loadFromEncodedString method that takes input as a String of an encoded message and converts it into a queue of Direction. Similar to the TargetQueue, the method
should throw an IllegalArgumentException if the syntax of the input is invalid. It is up to you to figure out when and where to throw exception, or otherwise to translate the string into the corresponding queue of Directions. I suggest you start by focusing on how to correctly parse very simple strings like 3[N]. Then move onto correctly parsing sequences of simple strings like 2[N]3[W] or more complicated strings such as 3[NE]. Finally, try to solve the problem of parsing nested strings such as 3[2[N]2[E]]. Please do not focus on getting this part to work to perfection before moving onto Part III of the assignment. You do not need this to be working to complete what comes next. In fact, you can still get a very high mark even if this part is only partially
2023-03-10