Homework 9: Pattern Matching Solution






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 les that don’t compile. Any compile errors will result in a 0.


  1. Do not include any package declarations in your classes.


  1. Do not change any existing class headers, constructors, instance/global variables, or method sig-natures.


  1. Do not add additional public methods.


  1. 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.)


  1. Always be very conscious of e ciency. Even if your method is to be O(n), traversing the structure multiple times is considered ine cient unless that is absolutely required (and that case is extremely rare).


  1. You must submit your source code, the .java les, not the compiled .class


  1. After you submit your les, redownload them and run them to make sure they are what you intended to submit. You are responsible if you submit the wrong les.



Pattern Matching


For this assignment you will be coding 3 di erent pattern matching algorithms: Boyer-Moore, Knuth-Morris-Pratt, and Brute Force. There is information about all three in the interface and more information about Boyer-Moore and KMP in the book (also under resources on T-Square). If you implement any of the three algorithms in an unexpected manner (i.e. contrary to what the Javadocs and PDF specify), you may receive a 0.


For all of the algorithms, make sure you check the simple failure cases as soon as possible. For example, if the pattern is longer than the text, don’t do any preprocessing on the pattern/text.




Failure Table Construction


The Knuth-Morris-Pratt (KMP) algorithm relies on using the pre x of the pattern to determine how much to shift the pattern by. The algorithm itself uses what is known as the failure table (also called failure function). There are di erent ways of calculating the failure table, but we are expecting one speci c format described below.


For any string pattern, have a pointer i starting at the rst letter, a pointer j starting at the second letter, a table called table that is the length of the pattern. Then, while j is still a valid index within pattern:




If the characters pointed to by i and j match, then write i + 1 to index j of the table and increment i and j.


If the characters pointed to by i and j do not match:






Homework 9: Pattern Matching                                                                           Due: See T-Square



{ If i is not at 0, then change i to table[i – 1]. Do not increment j or write any value to the table.


{ If i is at 0, then write i to index j of the table. Increment only j.



For example, for the string abacab, the failure table will be:


a b a c a b
0 0 1 0 1 2


For the string ababac, the failure table will be:


a b a b a c
0 0 1 2 3 0


For the string abaababa, the failure table will be:


a b a a b a b a
0 0 1 1 2 3 2 3


For the string aaaaaa, the failure table will be:


a a a a a a
0 1 2 3 4 5


Searching Algorithm


For the main searching algorithm, the search acts like a standard brute-force search for the most part, but in the case of a mismatch:



If the mismatch occurs at index 0 of the pattern, then shift the pattern by 1.


If the mismatch occurs at index j of the pattern and index i of the text, then shift the pattern such that index failure[j-1] of the pattern lines up with index i of the text, where failure is the failure table. Then, continue the comparisons at index i of the text (or index failure[j-1] of the pattern). Do not restart at index 0 of the pattern.



In addition, when a match is found, instead of shifting the pattern over by 1 to continue searching for more matches, the pattern should be shifted over by failure[j-1], where j is at pattern.length.




CharacterComparator is a comparator that takes in two characters. This allows you to see how many times you have called compare(). We will be looking at the number of times you call compare() while grading.


If you do not use the passed in comparator, this will cause tests to fail and will signi cantly lower your grade on this assignment.




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.








Homework 9: Pattern Matching Due: See T-Square
kmp 20pts
buildFailureTable 10pts
boyerMoore 20pts
buildLastTable 10pts
bruteForce 15pts
Checkstyle 10pts
E  ciency 15pts
Total: 100pts



A note on JUnits


We have provided a very basic set of tests for your code, in PatternMatchingStudentTests.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 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 Raymond Ortiz (rortiz9@gatech.edu) with the subject header of \CheckStyle XML”.




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:


Bad: throw new IndexOutOfBoundsException(“Index is out of bounds.”);


Good: throw new IllegalArgumentException(“Cannot insert null data into data structure.”);












Homework 9: Pattern Matching                                                                           Due: See T-Square





If available, use the generic type of the class; do not use the raw type of the class. For example, use new LinkedList<Integer>() instead of new LinkedList(). 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 Lambda Expressions Method References


If you’re not sure on whether you can use something, and it’s not mentioned here or anywhere else in the homework les, just ask.


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.




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


  1. java


This is the class in which you will implement the di erent pattern matching algorithms. Feel free to add private static helper methods but do not add any new public methods, new classes, instance variables, or static variables.


  1. java


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






Homework 9: Pattern Matching                                                                           Due: See T-Square



  1. java


This is a comparator that will be used to count the number of comparisons used. You must use this comparator. Do not modify this le.





You must submit all of the following le(s). Please make sure the lename matches the lename(s) below, and that only the following le(s) are present. T-Square does not delete les from old uploads; you must do this manually. Failure to do so may result in a penalty.


After submitting, 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. java

















































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