COMPUTER SCIENCE 12B
ADVANCED PROGRAMMING TECHNIQUES
PROGRAMMING ASSIGNMENT 6
Programming with Collections – Edit distance –
You are to write a client program that computes the edit distance between two words, i.e.,
the minimum number of operations needed to transform one string into the other.
For this program, an operation is a substitution of as single character, such as from
“brisk” to “brick”. The edit distance between the words “dog” and “cat” is 3, because the
chain of “dot”, “cot” and “cat” transforms “dog” to “cat”.
When computing the edit distance between two words, each intermediate word must be
an actual valid word. Edit distances are useful in applications that need to determine how
similar two strings are, such as spelling checkers.
Your program should ask the user for the name of a dictionary text file (we will provide
this). From this file, you should compute a map from every word to its intermediate
neighbors; that is, the words that have an edit distance of 1 from it. Once this map is
built, you can ask the user to enter two words to compare and you “walk” the map to find
paths from one word to another. This process should be done in a loop: once you
compute the edit distance of two words, you prompt again the user for the next two
A good way to process paths to walk the map is to use a linked list of words to visit,
starting from the beginning word, such as “dog” in the above example. Your algorithm
should repeatedly remove the front word of the list and add all of its neighbors to the end
of the list, until the ending word (such as “cat”) is found or until the list becomes empty,
which indicates that no path exists between the two words.
Special cases: (1) If a word is not included in the dictionary your program should print
out the message “Word does not exist”, (2) The edit distance of two words with different
length is not defined. Therefore, if the two words given as an input by the user do not
have the same length then your program should print the message “No solution”, (3) if
both cases (1) and (2) occur, you may print either error message.
You should download from LATTE two dictionary files. File text.txt has a dictionary
of 8 words. You can use it to the your program with the “dog”/”cat” example (among
others). File dict.txt is a larger file and you should use it to test your program with
more complex examples. We will be using this file for testing your programs.
You don’t need to create any classes for this part. You only need to write one client
program and you should name it EditDistance.java. You should however break your
program into methods (e.g., one that builds the map, show transformation paths,
calculates edit distance, etc)
You will be graded on correctness and programming style including the use of good
variable names, comments on each class and each method, using local variables when
possible, correct use of generics and the other standard style guidelines.
While you choose how you want to break your code up into methods, we choose how
your program needs to behave externally. You must follow the template we outline for
Your program should first ask the user for the name of a dictionary file on one line. Your
program should then loop through the following interactions, each of which should be on
a separate line.
1. Ask the user for two words separated by a single space for which to compute the
2. Print “Path = “ followed by each word in the edit path (starting with the first word
the user entered), a comma, a space, then the next word. A comma or a space
should not follow the last word.
3. Print “Edit distance = x”, where x is the edit distance.
Here is an example user interaction where everything in bold is input by the user, and
everything not in bold is output by your program.
Enter name of dictionary file: dict.txt
Enter two words separated by a space: dog cat
Path = dog, dot, cot, cat
Edit distance = 3
Enter two words separated by a space: brisk brick
Path = brisk, brick
Edit distance = 1
Enter two words separated by a space: transportation cat
Enter two words separated by a space: foobar whobar
Word does not exist
You may choose to implement a quit operating by listening for a single word from the
user, such as “quit”, if you would like, but you do not have to.
There are better algorithms for computing edit distance, but this approach runs
reasonably quickly even for a large dictionary like dict.txt. The slow part is
computing the neighbors, but that could be pre-computed and stored in a separate file.
The program uses a LinkedList as a queue to keep track of candidate words to explore. A
set is used to keep track of previously explored words. The algorithm keeps a count of
how many words are at each distance from the original word so that it can report the edit
distance. It also constructs a map each time it explores that keeps track of how it got to
each word. That allows the program to report the path between the two words. All in all,
this involves a LOT of data structure manipulation using the standard Java collections
You DON’T need to follow this design. You are free to design your own program as you
Your Java source code should be submitted via Latte the day it is due.
You will be graded on
o External Correctness: The output of your program should match exactly what is
expected. Programs that do not compile will not receive points for external
o Internal Correctness: Your source code should follow the stylistic guidelines
shown in class. Also, remember to include the comment header at the beginning
of your program.
o One-on-one interactive grading: By the end of the day that the assignment is
due, please make an appointment with your TA for an interactive 10-15 minute
grading session. You will receive an email notifying you of the name of the TA
who has been assigned to you for this assignment with further instructions on
setting up the appointment. (You will be meeting with a different TA for each
assignment). One-on-one interactive grading will help you improve your
programming skills and avoid repeating mistakes from one assignment to the