Problem Solving Assignment 3

Due Monday, January 29 at 11:59pm PST

There are two problems in this PSA.

Notes:

• This IS a pair assignment. You MUST do the assignment with your partner.

• You must complete an interview with a Lab Tutor for this PSA. Interviews are individual (partly to ensure that one partner doesn't do all the work). See instructions here for more details.

• This work should be done in its own directory called 'psa3'. Instructions here.

• This assignment has sample solution code that you can run on ieng6. You won't be able to see the java code itself =) but you will be able to do tests to see what it does, and make sure yours does the same thing. YOUR CODE MUST DO THE EXACT SAME THING. EXACT!! Wording, spaces, everything. Instructions on how to run the sample solution code are here .

• Each file must have a header with the team members' names, logins, and PIDs. The header should also describe the program in 2-3 sentences.

This homework requires skills from Chapter 1 through Chapter 3.

Problem 1

Make a program that will detect if an email message is spam.
Update 1/23/07 8:30pm: I changed the wording a little bit in the tips for finding "words" in the message, hopefully it is more clear. Also noted that the user is required to enter 4 words minimum (still 3 spaces, but it makes more sense then to have 4 words). Doesn't really change anything about the assignment.

Introduction:

• Everyone hates getting spam! Have you ever wondered why your email service (gmail, ucsd, hotmail, etc) can't tell that a message is spam and just not send it to you? That would save you a lot of time. Turns out, your email service probably already does do this, but it is a tough problem to solve and some will always get through. In this problem, we'll make a basic spam detector. It won't detect ALL spam, but don't worry, neither does Microsoft nor Google nor any other of the "pros"!
• Your program will detect two kinds of spam: Nigerian banking scams and shady prescription drug sales.

Details:

• Your program must be in a file called SpamKiller.java
• Ask the user to type in the email message to test (Notes: The user must enter a message that has at least 4 words. The user should type their message all on one line. See further detail below.)
• Then perform the following tests:
  • The first kind of spam we'll be detecting are the Nigerian banking scams. The characteristics we're looking for are:
    1. Every single letter in the message is upper case
    2. The word "NIGERIA" (any capitalization--Nigeria, nigeria, nIGeRia, etc) appears anywhere in the message, and the third word in the message is "URGENT" (again, any capitalization). (the message doesn't pass this test unless BOTH of these are true)
  • The next kind of spam we'll be detecting are shady prescription drug sales. These are the things you'll be looking for:
    1. The word "Viagra" (any capitalization) appears anywhere in the message, and The word "Rx" (with that capitalization only) appears in the first half of the message (don't care about the second half), and the word "Canada" (with that capitalization only) appears in the second half of the message (don't care about the first half) (a message doesn't pass this test unless ALL 3 of these are true)
    2. The message ends with at least two exclamation points in a row ("!!")
  • Of all four tests, if 2 or more of them pass, then you will tell the user that the message is spam. (it can be both Nigerian tests, or both prescription tests, or any combination) Otherwise, tell the user the message is not spam.
• For each of these tests, before you write any code, think about the basic algorithm that will solve this problem. It is a good idea to sketch the algorithm in pseudocode first. When you are confident that your algorithm will solve the problem, start up an editor and start coding!

Tips:

• The user should type in the message all on one line (it is ok if the text wraps around to go on multiple lines, but do not hit "Enter" until done typing in the whole email message).
• When looking at the first and second "half" of the message, don't worry about possibly cutting up a word that is on the boundary, that's fine. First and second half means, for example, if the string is 10 characters long (including spaces and everything), divide it into 5 and 5. For 11 characters, divide it into 5 and 6.
• When looking at the third word, we define a "word" to be whatever is between spaces. So the third word is whatever is between the second and third occurrences of " " in the message (even if it doesn't seem like a "word"--could be punctuation, numbers, etc). The user MUST enter a message that has at least 4 words (3 spaces). Don't worry about trying to handle if they don't (you'll notice less than 4 words [sometimes] "breaks" the sample solution). If you have any questions about weird cases, try them out on the sample solution or post on the WebBoard.
• Before you write any code, write a series of comments, each on their own line, that describe each thing you need to do (ask user for input, get input, each test, etc). Then go back and write the code that does that under the comment. This will help you focus and not feel overwhelmed while coding. (Be sure to leave them in, because these types of code section label comments belong in any well-written program! You've just saved yourself the trouble of going back after the fact to add them in.)
• You can see a sample solution by following these instructions.

Problem 2

Calculate and print statistics

Introduction:

• Your program must be in a file called Statistics.java

• The point is to make a program that reads a list of numbers and calculates the average, the minimum and the maximum number in the list.

• Your program should:

  • Read the length of the list of numbers (a positive integer)
  • If the number entered by the user is negative or zero, print the message "The List is empty! Exiting..." and exit the program
  • Ask the user to enter each number one by one. It can be a floating point or a whole number. Update 01/26/2007: Notice that each question should be of the format "Please enter the xyz number", where xyz should be 1st, 2nd,... 11th,.. 22nd,.. etc. It is OK if you just print number-th after number 3: 2nd, 3rd, 4th, .... 11th, .... 21th, 22th.. etc.
  • Output the minimum value of the list
  • Output the maximum value of the list
  • Output the mean value (average) of the list

Tips:

• The very first value entered is both the maximum and the minimum value. After that, you should check whether the maximum (so far) value is smaller than the value entered by the user (each step). If so, the new value is now the maximum. A similar check should be made comparing the value just entered and the minimum.
• Remember that the mean value is calculated by the division of the sum of elements by the number of elements.
• You can see a sample solution by following these instructions.

Details:

• Sample Execution:

  -bash-2.05b$ java Statistics
This program calculates the mean, maximum and minimum values of a list of numbers.

Please enter the length of the list
6
Please enter the 1st number
2.1
Please enter the 2nd number
3
Please enter the 3rd number
6.3
Please enter the 4th number
2.8
Please enter the 5th number
-3.3
Please enter the 6th number
100

Statistics:
Min = -3.3
Max = 100.0
Mean = 18.483333333333334


• Your program should behave exactly as the sample solution. Check here how to do this.

Details

Start by creating a directory (folder) in your ieng6 cs8fzz account (this is necessary for the bundle-psa3 script). After you log in, create a directory by typing the commands:

-bash-2.05b$ mkdir psa3

Go into that directory (like double clicking to open a folder) with the command:

-bash-2.05b$ cd psa3 

Note: you must name your directories (folders) and files as indicated in the problem descriptions for the turn in program to work.

In order to run the sample solution program you should invoke the following command:

-bash-2.05b$ runsample [classname]

So for this assignment, do:

-bash-2.05b$ runsample SpamKiller

or

-bash-2.05b$ runsample Statistics

This assignment is worth 20 points.

General (4 pts):
• 1 Point: For proper formatting in both SpamKiller.java and Statistics.java. Proper formatting means that your code is properly and consistently indented.
• 1 Point: For program documentation. You must write a 2-4 sentence description of the program (as a comment) that provides insight into what the program does and what it's useful for (in both SpamKiller.java and Statistics.java). In this header comment, you are also required to put the author names, author PIDs and author logins
• 2 points: Interview (done individually) see instructions here.

  SpamKiller.java (8 pts):

• 1 point: Correctly determine if message is in all caps
• 2 points: Correctly determine if message has the words Nigeria and urgent, as described
• 2 points: Correctly determine if message has the words Viagra, Rx and Canada, as described
• 1 point: Correctly determine if message ends in !!
• 2 points: Correctly determine if message is spam, and everything matches sample solution exactly

  Statistics.java (8 pts):

• 1 Point: Ask user to input the length of the list of numbers and take user's input.
• 2 Points: Ask user to input each number and take user's input
• 2 Point: Output words in correct places, matching sample solution output for where a new line starts, number of spaces, output of number location (4th.. etc).
• 1 Point EACH: Output the correct minimum, maximum and mean values

How to turn in your homework electronically

When you are ready to turn in your homework, run bundle-psa3 from your psa3 directory. The session should look like this:

-bash-2.05b$ cd ~/psa3
-bash-2.05b$ bundle-psa3
Good; all required files are present:

        SpamKiller.java
        Statistics.java

Do you want to go ahead and turnin these files? [y/n]y
OK.  Proceeding.


Performing turnin of approx. XXXX bytes 
Copying to /home/linux/ieng6/cs8w/turnin.dest/cs8wzz.psa2
.
Done.
Total bytes written: XXXX 
Please check to be sure that's reasonable.
Turnin successful.

If you want to make changes after you've turned in your homework, make the changes and run bundle-psa3 again. The program will warn you that a "previously turned-in file exists" and ask if "you wish to over-write this existing file" (delete the old version and replace it with this new one). Respond in the affirmative by typing y and pressing the Enter key.

10% of your grade on this assignment will come from an interview you will have with one of the tutors during Open Lab Hours. You have 48 weekday hours after the electronic turnin deadline to get your interview done. The deadline for the interview for PSA 3 is Wednesday, Jan 31, theoretically at midnight, but actually by the end of the last tutor hour scheduled. You get an interview by going into B260 during a scheduled tutor hour. Find the tutor, ask them if you can interview for PSA 3. If they have others who are waiting for interviews, your name will go on the end of the list of people waiting. Interviews take about 5 minutes each. It is your responsibility to go in early enough that you can get your interview completed. If everyone waits until the last hour on Wed, this will not work. The tutor will ask you to log in, change to the directory where your work is (psa3) and then to follow their directions. They will ask you to run your program to show that it works, open files in your favorite editor, and ask you questions about how your code works. Additionally, they may question you as to how you would (theoretically) make small changes to the program to have it do something slightly different. Learning to be able to explain your problem solving process and discuss code with another human being is a very important professional skill. We hope that this process will help you develop this skill.

Copying the assignment directory to partner's home directory

You can copy the psa3 directory and its files to your partner's home directory by:

bash% scp -r psa3 cs8wxx@ieng6.ucsd.edu:

(don't forget the colon at the end of the command) where cs8wxx is your partner's username. You must be in the parent directory of the psa3 directory. So, you if you are currently in the psa3 directory you should execute "cd ..". Similarly, if the psa3 direcory is in your home directory then you have to be in your home directory. If you aren't there just execute "cd ~" and you'll be there. Your partner is required to enter his password when you enter the scp command. To check if the copy worked, your partner must login and ckeck if the psa3 directory exists in his home directory and if the proper files are located in it. This can be done by executing: "ls ~/psa3". The files in the psa3 directory should be listed.

Redirecting the input and the output

You can redirect the input af a program by using the "<" symbol in the command line. Instead of reading the input from the standar input device (which is the keyboard):

bash% java SpamKiller < sampleEmail.txt

This command will redirect the input of the SpamKiller program to the file sampleEmail.txt. It will read the contents of the file as if they were given by pressing the buttons on keyboard. Similarly you can redirect the output af a program by using the ">" symbol in the command line. Instead of displaying the output on the standar output device (which is the computer monitor):

bash% java SpamKiller > outFile.txt

This command will redirect the output of the SpamKiller program to the file sampleEmail.txt. It will write the output in the "outFile.txt" file (all contents of the will be erased if file exists, if it doesn't exist, it will be created) as if they would be printed on the computer screen (so, you won't get any output on the screen). You can combine both redirections. For example you may have an email.txt file with a sample email, and also you want the results of the scan to be put on the file output.txt. This can be done by:

bash% java SpamKiller < email.txt > output.txt

Finding the differences between files

You can find the differences between two text files by using the diff command:

bash% diff filename1 filename2

The output will be the differences between the files. If there is no output at all that means that the files are identical.

Example: Testing the output of your program, can be completed in four steps, using the above tips.

Create a file with sample input (lets name it "input.txt" for your program (as if you would write it if the program was running)

Run your program and redirect the exit to a file: bash% java Statistics < input.txt > output1.txt

Run the provided program and redirect the exit to a second file: bash% runsample Statistics < input.txt > output2.txt

Check if there are differences between the two output files: bash% diff output1.txt output2.txt

Learning to use text editors

Vim

Run the command vimtutor, a separate program that will teach you to use Vim.

Emacs

Use the built-in tutorial by running emacs and, within the editor, typing CTRL-h t.

Pico

You can reach Pico's built-in help by typing CTRL-g. If you want further instruction, look at this Pico tutorial from NC State.