Homework 8: Sorting

Homework 8: Sorting
Important
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
files 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 signatures.
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 efficiency. Even if your method is to be O(n), traversing the structure
multiple times is considered inefficient unless that is absolutely required (and that case is extremely
rare).
7. You must submit your source code, the .java files, not the compiled .class files.
8. After you submit your files, redownload them and run them to make sure they are what you
intended to submit. You are responsible if you submit the wrong files.
Sorting
For this assignment you will be coding 5 different sorts: cocktail sort, insertion sort, selection sort, merge
sort, and LSD radix sort. You will also be coding the kth select algorithm that follows the quick sort
algorithm. In addition to the requirements for each sort, to test for efficiency, we will be looking at the
number of comparisons made between elements while grading.
Your implementations must match what was taught in lecture and recitation to receive
credit. Implementing a different sort or a different implementation for a sort will receive no credit even
if it passes comparison checks.
Comparator
Each method (except radix sort) will take in a comparator and use it to compare the elements of the
array in various algorithms described below and in the sorting file. You must use this comparator as
the number of comparisons performed with it will be used when testing your assignment.
Note that comparator.compare(x, y) is equivalent to x.compareTo(y).
Inplace Sorts
Some of the sorts below are inplace sorts. This means that the items in the array passed in aren’t copied
over to another array or list. Note that you can still create variables that hold only one item; you cannot
create another data structure such as array or list in the method.
Stable Sorts
Some of the sorts below are stable sorts. This means that duplicates should remain in the same relative
positions after sorting as they were before sorting.
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Homework 8: Sorting Due: See Canvas
Cocktail Sort
Cocktail sort should be inplace and stable. It should have a worst case running time of O(n
2
) and a
best case running time of O(n). Note: Implement cocktail sort with the optimization where it
utilizes the last swapped index. Remembering where you last swapped will enable some optimization
for cocktail sort. For example, traversing the array from smaller indices to larger indices, if you remember the index of your last swap, you know after that index, there are only the largest elements in order.
Therefore, on the next traversal down the array, you start at the last swapped index, and on the next
traversal up the array, you stop at the last swapped index. Make sure that both on the way up and on the
way down, you only look at the indices that you do not know are sorted. Do not make extra comparisons.
Example of one pass of cocktail sort with last swapped optimization:
Start of cocktail sort:
1 2 6 5 3 4 7 8 9
Start going up the array:
Compare 1 (at index 0) with 2 (at index 1) and don’t swap
1 2 6 5 3 4 7 8 9
Compare 2 (at index 1) with 6 (at index 2) and don’t swap
1 2 6 5 3 4 7 8 9
Compare 6 (at index 2) with 5 (at index 3) and swap
1 2 5 6 3 4 7 8 9
Compare 6 (at index 3) with 3 (at index 4) and swap
1 2 5 3 6 4 7 8 9
Compare 6 (at index 4) with 4 (at index 5) and swap
1 2 5 3 4 6 7 8 9
Compare 6 (at index 5) with 7 (at index 6) and don’t swap
1 2 5 3 4 6 7 8 9
Compare 7 (at index 6) with 8 (at index 7) and don’t swap
1 2 5 3 4 6 7 8 9
Compare 8 (at index 7) with 9 (at index 8) and don’t swap
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Homework 8: Sorting Due: See Canvas
1 2 5 3 4 6 7 8 9
Start going down the array:
Note: Skip over indices 5 - 8 since no swaps occurred there.
Compare 4 (at index 4) with 3 (at index 3) and don’t swap
1 2 5 3 4 6 7 8 9
Compare 3 (at index 3) with 5 (at index 2) and swap
1 2 3 5 4 6 7 8 9
Compare 3 (at index 2) with 2 (at index 1) and don’t swap
1 2 3 5 4 6 7 8 9
Compare 2 (at index 1) with 1 (at index 0) and don’t swap
1 2 3 5 4 6 7 8 9
Finished one pass of cocktail sort.
Note: Next time going up, skip over indices 0 - 2 since no swaps occurred there.
Insertion Sort
Insertion sort should be inplace and stable. It should have a worst case running time of O(n
2
) and a
best case running time of O(n).
Note that, for this implementation, you should sort from the beginning of the array. This means that
after the first pass, index 0 and 1 should be considered sorted. After the second pass, index 0-2 should
be considered sorted. After the third pass, index 0-3 should be considered sorted, and so on.
Selection Sort
Selection sort should be inplace. It should have a worst case running time of O(n
2
) and a best case
running time of O(n
2
).
Merge Sort
Merge sort should be stable. It should have a worst case running time of O(n log n) and a best case
running time of O(n log n).
Radix Sort
Radix sort should be stable. It should have a worst case running time of O(kn) and a best case running
time of O(kn), where k is the number of digits in the longest number. You will be implementing the
least significant digit version of the sort. You will be sorting ints. Note that you CANNOT change the
ints into Strings at any point in the sort for this exercise. The sort must be done in base 10. Also, as
per the forbidden statements section, you cannot use anything from the Math class besides Math.abs().
However, be wary of handling overflow if you use Math.abs()!
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Homework 8: Sorting Due: See Canvas
Kth Select
Kth select should be inplace. It should have a worst case running time of O(n
2
) and a best case running
time of O(n). Your implementation must be randomized as specified in the method’s javadocs. Logically,
it is similar to a one-sided quick sort. When asked for the kth smallest, you should return what would
be at the k − 1 index if the array was perfectly sorted.
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:
cocktailSort 10pts
insertionSort 10pts
selectionSort 10pts
mergeSort 15pts
lsdRadixSort 15pts
kthSelect 15pts
Other:
Checkstyle 10pts
Efficiency 15pts
Total: 100pts
A note on JUnits
We have provided a very basic set of tests for your code, in SortingStudentTests.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 Canvas under Files, 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 on Canvas, under
Files, along with instructions on how to use it. We will take off a point for every style error that occurs.
If you feel like what you wrote is in accordance with good style but still sets off the style checker please
email Tim Aveni (tja@gatech.edu) with the subject header of “[CS 1332] CheckStyle XML”.
Javadocs
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.
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Homework 8: Sorting Due: See Canvas
Vulgar/Obscene Language
Any submission that contains profanity, vulgar, or obscene language will receive an automatic zero on
the assignment. This policy applies not only to comments/javadocs but also things like variable names.
Exceptions
When throwing exceptions, you must include a message by passing in a String as a parameter. The message 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.");
Generics
If available, use the generic type of the class; do not use the raw type of the class. For example, use new
LinkedNode<Integer() instead of new LinkedNode(). 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.
• package
• System.arraycopy()
• clone()
• assert()
• Arrays class
• Array class
• Thread class
• Collections class
• Collection.toArray()
• Reflection APIs
• Inner or nested classes
• Lambda Expressions
• Method References (using the :: operator to obtain a reference to a method)
• Anything besides Math.abs() in the Math class (for this homework only)
• String class (for this homework only)
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Homework 8: Sorting Due: See Canvas
If you’re not sure on whether you can use something, and it’s not mentioned here or anywhere else in
the homework files, just ask.
Debug print statements are fine, 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 off points.
Provided
The following file(s) have been provided to you. There are several, but we’ve noted the ones to edit.
1. Sorting.java
This is the class in which you will implement the different sorting algorithms. Feel free to add
private static helper methods but do not add any new public methods, new classes, instance
variables, or static variables.
2. SortingStudentTests.java
This is the test class that contains a set of tests covering the basic operations on the Sorting 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.
Deliverables
You must submit all of the following file(s). Please make sure the filename matches the filename(s)
below, and that only the following file(s) are present. If you make resubmit, make sure only one copy of
the file is present in the submission.
After submitting, double check to make sure it has been submitted on Canvas and then download your
uploaded files to a new folder, copy over the support files, recompile, and run. It is your responsibility
to re-test your submission and discover editing oddities, upload issues, etc.
1. Sorting.java
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