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CS 455 Programming Assignment 4
Spring 2024 [Bono]
Due: Wednesday, Apr. 10, 11:59pm
Introduction and Background
In this assignment you will get a chance to use some of the Collection classes and methods we
have covered recently. This will enable you to write a faster-running program with less effort
than you would otherwise. In this assignment you will also get an opportunity to do your own
design; the design outline we provided you is less constrained than in past assignments: you
will be deciding on the exact interface and representation for your most of your classes. You'll
also get some practice with command-line arguments and text file processing.
This assignment concerns the game of Scrabble. You may know the game of Scrabble better
as Words with Friends. If you want to try out Words with Friends yourself you can download
the free app for your smartphone. However, the programming assignment is not to create the
game itself, but to write a console-based program that finds all possible words that can be
made from a rack of Scrabble tiles (so it could help someone playing Scrabble). We'll elaborate
on the exact requirements of this assignment in the section on the assignment below.
A rack of Scrabble tiles (the little number is the score for playing that tile)
Table of Contents
The assignment files
The assignment
Summary of requirements
Error Checking
Approach
The AnagramDictionary class
Finding all the subsets of the rack
Class design
Development hints / Test data
Grading criteria
README file / Submitting your program
The assignment files
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Note: the blurbs below do not describe what each of these classes are, and how they fit
together. For more details on that, see the section on the class design.
The starter files we are providing for you on Vocareum are listed here. The files in bold below
are ones you create and/or modify and submit. The ones not in bold are ones that you will
use, but not modify. More details about the java classes below are in the section on class
design. The files are:
WordFinder.java This class will contain the main method, and any other helper methods
that you design. (You create this file.)
AnagramDictionary.java All anagram sets from a dictionary. We have provided the
interface for you. This class is discussed more here.
Rack.java Stores the current rack. You can decide on the representation and public
methods for this class. We wrote the private static allSubsets method for you, discussed
later.
ScoreTable.java This class has information about how much each scrabble letter is worth.
(You create this file.)
IllegalDictionaryException.java A class for reporting an illegal dictionary. We wrote this for
you.
sowpods.txt The Scrabble dictionary we will be using. The version given here is all lower
case letters. Go here for an explanation of its odd name.
testFiles A subdirectory with some data files and corresponding output for help in
testing. The README.txt file in that directory explains the files and how to use them.
README See section on Submitting your program for what to put in it. Before you start the
assignment please read the following statement which you will be "signing" in the
README:
"I certify that the work submitted for this assignment does not violate USC's
student conduct code. In particular, the work is my own, not a collaboration,
and does not involve code created by other people or AI software, with the
exception of the resources explicitly mentioned in the CS 455 Course Syllabus.
And I did not share my solution or parts of it with other students in the
course."
Note: you may have additional files, see the section on the class design for more about this.
The assignment
You will be implementing a program, called WordFinder, that when given letters that could
comprise a Scrabble rack, creates a list of all legal words that can be formed from the letters
on that rack. To solve the problem you will also need a scrabble dictionary (we'll provide that
for you). Some particulars of the Scrabble dictionary: it only has words of length two or more,
and it includes all forms of a word as separate entries, e.g., singular plus plural, and verb
conjugations.
For example, if your rack had the letters c m a l you could rearrange the letters to form the
words calm or clam, but you could also form shorter words from a subset of the letters, e.g., lam
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or ma. It's generally difficult to figure out all such sequences of the letters that form real words
(unless you are a tournament Scrabble competitor who knows the Scrabble dictionary very
well).
For your program, you will display all such words, with the corresponding Scrabble score for
each word, in decreasing order by score. Each letter has a score associated with it, the score
for a word is the sum of the scores of each letter in that word. For words with the same
scrabble score, the words must appear in alphabetical order. Here are the results for a rack
consisting of "cmal" (using the sowpods dictionary) shown in the output format you will be
using for your program (user input is shown in italics):
Rack? cmal
We can make 11 words from "cmal"
All of the words with their scores (sorted by score):
8: calm
8: clam
7: cam
7: mac
5: lac
5: lam
5: mal
4: am
4: ma
2: al
2: la
We'll provide you the Scrabble score for each letter later in this document.
Here's more about exactly how to run your program and what happens:
Your program will take an optional command-line argument for the dictionary file name. If
that argument is left off, it will use the Scrabble dictionary file sowpods.txt (see assignment files)
from the same directory as you are running your program. (Note: Required error-checking
related to the dictionary file is described in the following section.)
Once the program starts it will print the message:
Type . to quit.
Then the program will run in a loop on the console, printing the prompt "Rack? " (as seen in
the earlier example) and reading and processing each rack you enter, until you tell it to exit.
The user tells the program to exit by typing in "." at the prompt (i.e., a period). We aren't use a
command such as "quit" as the sentinel, since that could be a legal rack.
We have provided you a few sample data files, and corresponding correct reference output
from running those on the sowpods.txt (the Scrabble dictionary given) in the testFiles
directory. Please see the README.txt in that directory for guide to the sample files and how to
use them. Your output must match the reference output character by character.
The real game of Scrabble has only upper-case letters on tiles, but for our program we'll
accept any sequence of non-whitespace characters as a legal "rack." However, words will only
be able to be formed from actual letters if that's what's in the given dictionary. E.g., if the rack
given is "abc@" you will report the words such as "cab", but there will be no words containing
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"@", since @ doesn't appear in any dictionary words. If there are such characters in the rack,
they also get printed out in the initial message displayed about the rack. E.g, ??We can make 11
words from "cm!a#l"
The program will work on both lower-and-upper case versions of dictionaries, but all
processing will be case-sensitive. E.g., if the dictionary given has only upper-case versions of
words, it will find words from a rack such as "CMAL", but won't be able to find any words from
the rack "cmal".
Some other differences between this program and Scrabble:
The real game of Scrabble also has two blank wild-card tiles. Your program will not have
this feature.
In Scrabble you almost always have a rack of exactly seven letters. For this program you
can enter any number of characters for a rack. If the rack has more than seven characters,
you will report words from the dictionary that have more than seven characters too.
This program just deals with forming words only from what's on the rack, it doesn't
consider any tiles that are on the Scrabble board.
This shows how to run your program:
java WordFinder [dictionaryFile]
Note: in this common format for showing Unix command-line syntax the square brackets (i.e.,
[]) are not part of the command that is typed: it is just a notation indicating that the command
line argument shown is optional.
Additional program requirements are described in the following sections and summarized
here:
Approach. you are required to use the second approach discussed below, under
Approach. The class design we started goes along with that approach.
Efficiency. you will get more credit if you have an efficient solution. We discuss the
efficiency of the approach you are required to use in the sections on Approach and the
one that follows that on the AnagramDictionary class.
Class design. you are required to design and implement the classes discussed in the
section on class design. We will also be evaluating the quality of the fleshed out version
of this design.
Error checking. the two errors you have to handle are described in the next section.
README. as usual, you are required to submit a README file. See the end of this document
for what needs to go in it for this assignment.
Style / Documentation / Design. Also as usual, your program will be evaluated on style
and documentation; but this time we will also be evaluating your design. See the section
on grading criteria for more details.
Error checking
The only errors your program is required to check for are listed below. For each of these errors
your program will print the error message shown by example, then print
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Exiting program.
and then exit immediately.
1. The dictionary file does not exist.
Suppose the dictionary file given was testFiles/foobar.txt
Error message:
ERROR: Dictionary file "testFiles/foobar.txt" does not exist.
2. The dictionary file has duplicate words in it.
Suppose the dictionary file contained the word "cat" in two places. E.g., dictionary file
contents:
house
cat
the
dog
cat
doggy
Error message:
ERROR: Illegal dictionary: dictionary file has a duplicate word: cat
Your program does not have to report all duplicate words, just the first one it detects.
The example given above doesn't have any other words duplicated ("dog" and "doggy"
are two different words).
Approach
There are two distinct ways to approach this problem. One is to read in the dictionary, and
then for each rack given, compare each word in the dictionary to that rack to figure out
whether that word can be formed from some or all of the letters in that rack, creating a list of
the legal words as you go. This is faster to process the dictionary, but slower to process each
rack.
The second approach, which is the one you will be using for the assignment, involves
preprocessing the dictionary so that you organize the words by the set of letters each one
contains (this set is actually a multiset, because letters can appear more than once in a word;
the rack itself is also a multiset). Then for each rack you'll generate all the subsets of that
multiset of letters, and for each subset add all the words from the dictionary that have exactly
the same elements as that subset. This is slower to process the dictionary, but once we do this
processing, it's faster to process each rack than the first approach. This approach is explained
in more detail in the following two sections.
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It's a little complicated to describe in big-O terms the time for each approach, but what makes
the first approach slower for processing one rack is traversing the whole dictionary (which will
typically be large) for each rack. For the second approach, the slow part of processing a rack is
creating all the subsets. The worst case for creating the subsets is if there are no repeated
letters in the rack (i.e., largest number of subsets created). Even though generating the subsets
for such a rack would take O(n * 2n
) for a rack of n unique characters (because there are 2n
subsets when there are no repeat characters, and n n steps to form each subset), n will
typically be small: for a 7-tile rack: 27
 is only 128, times 7 is 896). In an instrumented solution
we wrote using this approach, processing the sowpods dictionary took under half a second,
and processing a 7-character rack with no repeating characters, and consisting of the most
commonly occurring letters in English took under 15 milliseconds (this is test file
testFiles/aestnlr.in). (Commonly occurring letters will result in a larger resulting word list.)
These runs were done on Vocareum.
Some of the time spent for processing a rack in the second approach is to get the list of
anagrams for each subset; we'll discuss that further in the next section.
The rest of the time spent processing a rack is to sort the resulting word list.
For full credit on this assignment you'll need to use this second approach for the assignment;
we'll go into further details about it in the following sections.
The AnagramDictionary class
For the approach we're using, we said that you would organize the dictionary words by the
(multi)set of letters a word contains. If two words contain the same exact letters in a different
order, they are called anagrams of each other. If a rack (or subset of that rack) has all the same
letters (and multiplicity of those letters) as a particular word in the dictionary, that word, plus
all of its anagrams from the dictionary should all be added to the list of words reported by our
WordFinder program.
You are required to create an AnagramDictionary class to handle this. It will have a getAnagramsOf
method that finds all anagrams of a particular string efficiently. For, example, suppose we have
a variable, dictionary, of type AnagramDictionary, that contains data from the sowpods dictionary.
If we did the call
dictionary.getAnagramsOf("rlee")
it would return an ArrayList of the following dictionary words: ["leer", "lere", "reel"] (not
necessarily in that order). Note, "rlee" is not a real word: the method does not require you to
pass it a word. But the anagrams returned are real English words.
How to do this efficiently? One insight is that if we put two words into some kind of canonical
form, then we could figure out if they are anagrams of each other by just comparing the
canonical versions of them for equality. This canonical form will be a sorted version of the
characters in the word. In the earlier example given the rack contained "cmal". The sorted
version of this rack is "aclm". The first two words listed in the output are "calm" and "clam",
anagrams of "aclm", or put another way, these first two words are the only dictionary words
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we can make using all the letters on the rack, and all the other words listed are anagrams of
subsets of "cmal".
For full credit your AnagramDictionary is required to find all the anagrams of one String in time
linear in the size of the output set (not including the time to sort the letters in the String given
to put it into canonical form.)
Finding all the subsets of the rack
Finding all subsets of a multiset is a somewhat difficult recursion problem on its own, so to
make this assignment easier, we wrote the code for you to do that (static method allSubsets in
Rack.java). The method is static because, like some other recursive methods we have written, it
takes all of its data as explicit parameters; also, this means allSubsets works regardless of what
representation you choose for your Rack objects (allSubsets will not be accessing any Rack
instance variables). The solution is similar in structure to the method to compute all
permutations of a string given in Section 13.4 of the textbook. You will likely have to write a
wrapper method that calls allSubsets with the correct starting parameters.
The allSubsets method uses a particular representation for the rack which we'll explain with an
example here. Earlier we mentioned that a rack is a multiset of letters (set because we don't
care about the order of the letters, and multiset because letters can appear more than once).
Suppose our rack is:
a b a d b b
Gathering together the like letters, we could rewrite this as "aabbbd". We could also say that
'a' appears with multiplicity 2, 'b' appears with multiplicity 3, and that 'd' appears with
multiplicity 1. allSubsets expects the rack information to be in two parallel arrays: one has the
unique letters, and the other has the multiplicity of that letter at the same array index. The
array of unique letters is actually a String, so we can do String operations on it. For the
example given, we could create this rack representation as follows:
// create variables for the rack "aabbbd"
String unique = "abd";
int[] mult = {2, 3, 1};
// example to show relation between values in unique and mult:
for (int i = 0; i < unique.length(); i++) {
System.out.prinln(unique.charAt(i) + " appears " + multi[i] + " times in the rack");
}
Like other examples of recursion over an array that we've seen, allSubsets will take a third
argument, k, which is the starting position of the part of the array that this recursive call will
process. So for this code, it's the starting postion from which to find the subsets. So, for
example, if we called
allSubsets(unique, mult, 1); // starts at position 1 in unique and mult
it would find all the subsets of the rack "bbbd" (i.e., it wouldn't consider the subsets that
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included any 'a's in it).
Class design
Unlike the previous programs in this course, this time you are going to design your own
classes, with some guidance. Consequently, part of your style score will be based on the
quality of your design.
When doing an object-oriented design, you first come up with a candidate set of classes,
choosing a name for each, and identifying the responsibilities of each in the context of the
larger program overall. We have done that step for you here. We are requiring you to have at
least the following five classes in your solution, with the responsibilities described. You are
allowed to add more classes to your design as you see fit. The five, with their overall
responsibilities described, are:
WordFinder
This contains the main method. This class will have a main that's responsible for
processing the command-line argument, and handling any error processing. It will
probably also have the main command loop. Most of the other functionality will be
delegated to other object(s) created in main and their methods.
Rack
This corresponds to the idea of the rack in the problem description. Thus, wherever your
program is using a rack, it should be using an object of type Rack. As previously
discussed, we have already provided the code for a private static Rack method allSubsets.
AnagramDictionary
This will contain the dictionary data organized by anagrams. It is required to have at least
the two public methods whose headers are given in the starter file. You are allowed to
add other methods to this interface. This class was discussed in more detail in the section
about it.
ScoreTable
This class has information about Scrabble scores for scrabble letters and words. In
scrabble not every letter has the same value. Letters that occur more often in the English
language are worth less (e.g., 'e' and 's' are each worth 1 point), and letters that occur
less often are worth more (e.g., 'q' and 'z' are worth 10 points each). You may use hard?coded values in its data. Here are all the letter values:
(1 point)-A, E, I, O, U, L, N, S, T, R
(2 points)-D, G
(3 points)-B, C, M, P
(4 points)-F, H, V, W, Y
(5 points)-K
(8 points)- J, X
(10 points)-Q, Z
This class should work for both upper and lower case versions of the letters, e.g., 'a' and
'A' will have the same score. Hint: You can index an array with a char that is a lower case
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letter by treating it as an int and subtracting 'a' from it (because the internal numeric
codes for letters are all sequential). E.g., If your letter is 'd', ('d' - 'a') = 3 and if it's 'e', ('e' -
'a') = 4.
IllegalDictionaryException
An exception that can be thrown by AnagramDictionary (see comments in
AnagramDictionary.java for details). We already wrote it for you.
Although you haven't done much class design yourself, you have seen many examples of well?designed classes in the textbook, lecture, labs, and assignments in this class. We recommend
you review the following sections of the textbook that give hints on deciding what classes and
methods would make sense for a program design, before you start on your own design: 8.1,
8.2, 12.1, and 12.2 (the last two of these were not in the original readings).
One thing to keep in mind is you want the code that operates on some data to be in the same
class that contains that data. One sign that your design doesn't have that feature is if your
classes tend to have a lot of get and set methods and not much else. That would indicate that
all the code operating on this data is outside of the class itself.
Hopefully we've made clear the importance of making all instance variables private. But even if
you make your data private there are other ways to expose the implementation of your
objects. For example, if you have a class that contains an ArrayList, and also provide an
accessor method for this ArrayList, it gives clients the ability to change the contents of that
arraylist from outside of the object methods, possibly invalidating the object. (We discussed
these types of issues and how to cope with them in the material on side effects in week 6.)
You are welcome to add additional classes as part of your design. These ones would be
designed and implemented by you, of course. If you have more classes, just make sure the
additional .java files are in your Vocareum home directory when you submit the assignment. If
a class is just used by one other class, you could put it in the same file as that class, or a
separate file. If it is used by multiple classes, it should be in its own file. Make sure you discuss
these additional classes in your design write-up in your README (including telling us where to
find them).
Development hints / Test data
As usual, we recommend creating test drivers for any non-trivial class you implement to make
it easier to debug your code. That should be pretty easy here, because the classes are
somewhat independent from each other. (WordFinder is an exception since it already is a main
program.)
You'll want to test your complete program (and your AnagramDictionary) on a small dictionary
file before subjecting it to sowpods.txt. We provided a sample small dictionary and input and
corresponding output for some racks in the testFiles directory (more about that in the next
paragraph). If you find AnagramDictionary-related bugs, you may want to use an even tinier
dictionary for when you are single-stepping, etc.
Once you have all your modules working, you can also check if your program produces the
right answers for sowpods.txt with the other test input files and corresponding output in the
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testFiles directory. Note: The testFiles/README.txt file describes what's what that directory.
Grading criteria
This program will be graded approximately 2/3 on correctness, 1/3 on design, style, and
documentation. As usual we will be using the style guidelines published for the class. There
was more about design issues in the section on class design in this document. Another issue
that will come into play is effective use of the parts of the Java library we have learned about.
E.g., it's better to use one of the Java sort methods than reimplementing it.
README file / Submitting your program
Your README file must document known bugs in your program, contain the signed certification
shown near the top of this document, and contain any special instructions or information for
the grader.
In addition, for this assignment, your README must also document your design. This includes
the approach you took to solving the problem (i.e., description of the data structures and
algorithms involved). One part of this was discussed in the section on approach. You will also
include there information about how your class design relates to this approach, including what
data structures and algorithms are encapsulated in which of your classes.
When you are ready to submit the assignment press the big "Submit" button in your PA4
Vocareum work area. Because you may have additional files in your program, it will try to
compile all files in your work area, and test the resulting program on the small dictionary data
we gave you in testFiles (not on sowpods). As usual, you will want to submit for the first time
well before the final deadline, so you have time to fix any errors you get on the submit script.
Passing these submit checks is not necessary or sufficient to submit your code (the graders
will get a copy of what you submitted either way). (It would be necessary but not sufficient for
getting full credit.) However, if your code does not pass all the tests we would expect that you
would include some explanation of that in your README. One situation where it might fail
would be if you only completed a subset of the assignment (and your README would
document what subset you completed.)

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