Description
Stacks and Queues
You are to code the following:
1. A Stack backed by a singly-linked list without a tail reference.
2. A Stack backed by an array
3. A Queue backed by a singly-linked list with a tail reference
4. A Queue backed by an array
A Stack is a last-in, first-out (LIFO) data structure; the last item to be inserted is the first item to be
removed. A Queue is a first-in, first-out (FIFO) data structure; the first item inserted is the first item to
be removed.
All your data structures must follow the requirements stated in the javadocs of each method you must
implement.
Note that the linked versions of the data structures should NOT be circular.
Capacity
The starting capacity of the array classes should be the constant INITIAL CAPACITY defined in the .java
files. Reference the constant as-is. Do not simply copy the value of the constant. Do not change the
constant.
If, while adding an element, the array class does not have enough space, you should regrow
the backing array to twice its old capacity. In other words, after one resize, the backing array’s length
should be INITIAL CAPACITY * 2, and after two resizes, it should be INITIAL CAPACITY * 2 * 2. Do
not resize the backing array when removing elements.
Removing
With both array classes, when elements are deleted from the array, the index the element was removed
from should be set to null. All unused positions in the backing array must be set to null.
Circular Arrays
The backing array in your ArrayQueue implementation must behave circularly. This means the front
variable might wraparound to the beginning when you remove to take advantage of empty space while
maintaining O(1) efficiency for all operations.
For this assignment, the front variable in ArrayQueue should represent the index that holds the next
element to dequeue. Failure to follow this convention will result in major loss of points.
For enqueuing, add to the back of the queue.
To access the back of the queue, you can add the size
to the front variable to get the next index to add to, though you will have to account for the circular
behavior yourself. If there are empty spaces at the front of the array, the back of the queue should wrap
around to the front of the array and make use of those spaces.
For dequeuing, you should simply treat the next index in the array as the new front. Do not shift any
elements during a remove.
When resizing the backing array, “unwrap” the data. Realign the queue with the front of the new
array during the transfer. The front variable of the queue is once again at index 0.
Homework 2: Stacks and Queues
Additionally, after removing the last element in the queue, move the front variable like you normally
would. Do not explicitly reset it to 0. This effectively means that going from size 1 to size 0 should not
be a special case for your code.
The examples below demonstrate what the queue should look like at various states.
In the example below, the queue begins empty (initial state). An element is added.
In the example below, adding to the back causes the newly added element to wrap around to the front.
In the example below, adding another element causes the queue to resize. The array capacity is doubled
and the front element moves to index 0.
In the example below, the last element of the queue is removed, but front moves as expected. The front
variable is not explicitly set to 0.
Homework 2: Stacks and Queues
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.
Methods:
ArrayStack constructor 1pts
ArrayStack push 7pts
ArrayStack pop 6pts
ArrayStack peek 4pts
LinkedStack push 6pts
LinkedStack pop 7pts
LinkedStack peek 4pts
ArrayQueue constructor 1pts
ArrayQueue enqueue 10pts
ArrayQueue dequeue 8pts
ArrayQueue peek 4pts
LinkedQueue enqueue 6pts
LinkedQueue dequeue 7pts
LinkedQueue peek 4pts
Other:
Checkstyle 10pts
Efficiency 15pts
Total: 100pts
Provided
The following file(s) have been provided to you. There are several, but we’ve noted the ones to edit.
1. ArrayStack.java
This is the class in which you will implement the ArrayStack. Feel free to add private helper
methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
2. LinkedStack.java
This is the class in which you will implement the LinkedStack. Feel free to add private helper
methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
3. ArrayQueue.java
This is the class in which you will implement the ArrayQueue. Feel free to add private helper
methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
4. LinkedQueue.java
This is the class in which you will implement the LinkedQueue. Feel free to add private helper
methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
5. LinkedNode.java
This class represents a single node in the linked list. It encapsulates the data and the next
reference. Do not alter this file.
6. StackStudentTest.java
This is the test class that contains a set of tests covering the basic operations on the Stack classes.
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.
7. QueueStudentTest.java
This is the test class that contains a set of tests covering the basic operations on the Queue classes.
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 file(s) to the course Gradescope. Make sure all file(s) listed below
are in each submission, as only the last submission will be graded. Make sure the filename(s) matches the
filename(s) below, and that only the following file(s) are present.
Do NOT submit LinkedNode.java
for this homework; if you do, your homework will not compile on Gradescope. If you resubmit, be sure
only one copy of each file is present in the submission. If there are multiple files, do not zip up the files
before submitting; submit them all as separate files.
Once submitted, double check that it has uploaded properly on Gradescope. To do this, download
your uploaded file(s) to a new folder, copy over the support file(s), recompile, and run.
It is your sole
responsibility to re-test your submission and discover editing oddities, upload issues, etc.
1. ArrayStack.java
2. LinkedStack.java
3. ArrayQueue.java
4. LinkedQueue.java
