Problem Set 1

part I due by 10:00 p.m. on Wednesday, June 25, 2025
part II due by 10:00 p.m. on Thursday, June 26, 2025

Preliminaries

In your work on this assignment, make sure to abide by the policies on academic conduct.

If you have questions while working on this assignment, please come to office hours, post them on Ed Discussion, or email cscis111-staff@lists.fas.harvard.edu.

Make sure to submit your work on Gradescope, following the procedures found at the end of Part I and Part II.

Part I

35 points total

Creating the necessary folder

1. If you haven’t already created a folder named s111 for your work in this course, follow these instructions to do so.

2. Then create a subfolder called ps1 within your s111 folder, and put all of the files for this assignment in that folder.

Creating the necessary file

The problems from Part I will all be completed in a single plain-text file. To create it, you should do the following:

1. Access the template that we have created by clicking on this link and signing into your Google account as needed.

2. When asked, click on the Make a copy button, which will save a copy of the template file to your Google Drive.

3. Select File->Rename, and change the name of the file to ps1_partI.

4. Add your work for the problems from Part I to this file.

5. Once you have completed all of these problems, choose File->Download->PDF document, and save the PDF file in your ps1 folder. The resulting file (ps1_partI.pdf) is the one that you will submit. See the submission guidelines at the end of Part I.

Problem 1: Picobot in an empty room

7 points; pair-optional

This is one of only two problems from this assignment that you may complete with a partner. See the rules for working with a partner on pair-optional problems for details about how this type of collaboration must be structured.

Develop a set of rules that cause Picobot to completely cover an empty square room, regardless of where it starts within the room.

You may find it helpful to review the material on Picobot in the lecture notes.

Open the Picobot simulator, and modify/replace the existing rules with your own rules until you can get it to work. Whenever you modify the rules, be sure to click the Enter rules for Picobot button before you click Go.

As discussed in lecture, you cannot include repeat rules – two or more rules that would both be triggered by a given combination of state and surroundings.

When you are satisfied with your rules, copy them into the ps1_partI file that you created following the guidelines above. We encourage you to include comments that describe your rules. These comments should be preceded by a # symbol. For example:

# The following rule tells Picobot to ...

Hints:

• One possible approach is to begin with the four rules that are present in Picobot when you first load it in your browser. Try those rules on several different starting positions by repeatedly clicking the Reset button and then the Go button.

  Ask yourself: What portion of the overall task do these initial rules accomplish? What remains to be done? Then try to add rules that will cause the robot to move in ways that will complete the overall task of covering/vacuuming the entire room. You will also need to revise the second rule so that it doesn’t cause the robot to crash when it has a wall to its west.

• It’s worth noting that it’s perfectly okay if your new rules cause the robot to revisit portions of the room that it has already covered. More generally, your rules do not need to be efficient!

Optional extra challenge

for personal gratification only!

At the heart of computer science are questions of complexity and efficiency: questions about how simple, fast, etc. the solution to a problem can be. For an optional challenge, see if you can create a solution for problem 1 that uses only 6 rules! If you are able to do so, include them in the separate section provided in ps1_partI.

Note: Because reducing the number of rules to 6 is a completely optional challenge, we will not be answering questions about how to do so!

Problem 2: Picobot in a maze

13 points; pair-optional

This is one of only two problems from this assignment that you may complete with a partner. See the rules for working with a partner on pair-optional problems for details about how this type of collaboration must be structured.

Develop a set of rules that enable Picobot to completely navigate a connected maze with corridors one square wide, regardless of its starting point. You can obtain an example of such a maze by opening the Picobot simulator and clicking on the right-arrow (-->) button below the lower right-hand corner of the room, which will show you this maze:

Modify/replace the existing rules with your own rules until you can get it to work. Whenever you modify the rules, be sure to click the Enter rules for Picobot button before you click Go.

As discussed in lecture, you cannot include repeat rules – two or more rules that would both be triggered by a given combination of state and surroundings.

When you are satisfied with your rules, copy them into your ps1_partI file. We encourage you to include comments that describe your rules. These comments should be preceded by a # symbol, as described in the earlier problem.

Hint: We strongly recommend that you take the approach outlined in lecture, which involves:

• using the right-hand rule
• having four states – one for each direction in which the robot could be facing
• starting with at least three rules for each state: one for when the wall is on your right and you are able to move, one for when you “lose the wall,” and one or two rules for hitting a dead end – i.e., for when you can no longer make progress in the current direction because there’s a wall in front of you.

Optional extra challenge

for personal gratification only!

See you if you can create a solution for problem 2 that uses only 8 rules. This is extremely challenging, and we don’t recommend starting with only 8 rules! Rather, begin by having at least 3 rules for each state as discussed in lecture, and then see if you combine rules in some way. If you are able to come up with a set of 8 rules that works, include them in the separate section provided in ps1_partI.

Note: Because reducing the number of rules to 8 is a completely optional challenge, we will not be answering questions about how to do so!

Problem 3: Java programming basics

9 points; individual-only

1. As discussed in lecture, there are a number of basic rules that all Java programs must follow. These rules are part of the syntax of the language. The following Java program violates several of these rules:

   public class BuggyProgram {
       public void main(String[])
           System.out.println("Help! This program is buggy.)
           System.out.println("Please find and fix the bugs.")
       }
   }
   

   Determine and fix all of the problems with this program. You may find it helpful to test your revised program in VS Code by entering it in the text editor and seeing if it compiles and runs. If you do this, remember that you will need to give the program file an appropriate name that is based on the name of the class.

   Once you are confident that you have fixed all of the problems in the code, put the revised program in your ps1_partI file as your answer to this question.

2. Class and method names must be valid Java identifiers. Which of the following names are not valid identifiers?

   airForce1
   static
   second Option
   mainStreet
   first_name
   3muskateers
   

   Explain your answer briefly.

3. What series of println statements would produce the following output? Make sure to include any escape characters that are needed within the string literals.

   "You're in.", Heidi told one of the designers.
   She continued, "And that means you're out."
   -----\\\\\/////-----
   

Problem 4: Flow of control

6 points; individual-only

What is the output of the following program? (Try to determine the answer before you actually run the program!)

public class Flow {
    public static void A() {
        C();
        System.out.println("scratch");
    }

    public static void B() {
        System.out.println("meow!");
        A();
    }

    public static void C() {
        System.out.println("cat");
    }

    public static void D() {
        C();
        A();
    }

    public static void main(String[] args) {
        A();
        B();
        D();
    }
}

Submitting your work for Part I

Submit your ps1_partI.txt file by taking the following steps:

1. Login to Gradescope by clicking the link in the left-hand navigation bar.

2. Click on the box for CSCI S-111.

3. If you still need to create a PDF file, open your file on Google Drive, choose File->Download->PDF document, and save the PDF file in your ps1 folder.

4. Click on the name of the assignment in the list of assignments on Gradescope. You should see a pop-up window labeled Submit Assignment. (If you don’t see it, click the Submit or Resubmit button at the bottom of the page.)

5. Choose the Submit PDF option, and then click the Select PDF button and find the PDF file that you created. Then click the Upload PDF button.

6. You should see a question outline along with thumbnails of the pages from your uploaded PDF. For each question in the outline:

   • Click the title of the question.
   • Click the page(s) on which your work for that question can be found.

   As you do so, click on the magnifying glass icon for each page and doublecheck that the pages that you see contain the work that you want us to grade.

7. Once you have assigned pages to all of the problems in the question outline, click the Submit button in the lower-right corner of the window. You should see a box saying that your submission was successful.

Part II

30 points total

Problem 5: Using procedural decomposition to print a phrase

30 points; individual-only

In this problem, you will write a program that tests your understanding of Java program structure, println statements, static methods, and procedural decomposition. You should limit yourself to the aspects of Java that are covered in Unit 1 of the coursepack, even if you are already aware of other programming constructs that could be useful. You may find it helpful to consult the example programs.

Your task is to display the phrase GOING GOING GONE using block letters that are created by sequences of println statements. The letters should be displayed vertically as follows:

+------
|
|
|   --+
|     |
|     |
+-----+

+-----+
|     |
|     |
|     |
|     |
|     |
+-----+

---+---
   |
   |
   |
   |
   |
---+---

|     |
|\    |
| \   |
|  \  |
|   \ |
|    \|
|     |

+------
|
|
|   --+
|     |
|     |
+-----+





+------
|
|
|   --+
|     |
|     |
+-----+

+-----+
|     |
|     |
|     |
|     |
|     |
+-----+

---+---
   |
   |
   |
   |
   |
---+---

|     |
|\    |
| \   |
|  \  |
|   \ |
|    \|
|     |

+------
|
|
|   --+
|     |
|     |
+-----+





+------
|
|
|   --+
|     |
|     |
+-----+

+-----+
|     |
|     |
|     |
|     |
|     |
+-----+

|     |
|\    |
| \   |
|  \  |
|   \ |
|    \| 
|     |

+------
|
|
+------
|
|
+------

Getting started

1. If you haven’t already done so, create a folder named ps1 for your work on this assignment. You can find instructions for doing so here.

2. In VS Code, select the File->Open Folder or File->Open menu option, and use the resulting dialog box to find and open your ps1 folder. The name of the folder should appear in a new Explorer pane on the left-hand side of the VS Code window.

3. Select File->New Text File, which will open up an empty window known as an editor window for your new program. It will initially have a name that is something like Untitled-1.

4. Select File->Save, and give the file the following name:

   BlockLetterWriter.java
   

   Important: When naming a Java file, the case of the letters matters. Make sure to use the exact combination of upper-case and lower-case letters that we have specified.

Part II requirements

Correctness
The output of your program should exactly match the output shown above. In particular:

• Each block character should be 7 lines in height.
• There should be a single blank line between the block characters in a given word (e.g., between the G and O in GOING).
• There should be five blank lines between words (e.g., between GOING and GONE).
• There should be one blank line at the end of the entire phrase.
• The horizontal lines in the block letters should be constructed using hyphens (-).
• The vertical lines in the block letters should be constructed using the vertical bar (|) character, which is found above the Enter or Return key on most keyboards. (Note: On some browsers, the vertical bar characters shown above will blend together into a single vertical line, but in VS Code there should be breaks visible between the vertical bars.)

• There should be no spaces at the end of any of the string literals that you print, and there should be no unnecessary spaces at the beginning of a string literal. For example, the string literal used to print the second line of a block letter I should be

  "   |"
  

  – i.e., exactly three spaces, followed by a vertical bar character, with no spaces after the vertical bar.

A text file with the expected output is available here.

Procedural decomposition
In order to receive full credit, your solution must use procedural decomposition — breaking the larger problem of displaying the phrase GOING GOING GONE into subproblems, and using static methods to solve the subproblems. More specifically, you should use static methods:

• to capture the structure of the solution. For example, you should have a separate method for each letter in the phrase. However, having a separate method for each letter alone is not enough. Rather, you should also come up with other ways in which a method would help you to capture structure.

• to eliminate code duplication. Typically, you wouldn’t create a method to avoid repeating just one or two println statements. However, if a specific group of four or more println statements is repeated, you should create a separate method for those four or more statements.

Don’t forget that methods can call other methods as needed.

Other requirements

• Put your program in a class named BlockLetterWriter, which means that you will need to store it in a file named BlockLetterWriter.java.
• Include a comment at the top of the file that includes your name, your email address, and a short description of the program.
• Include a brief comment before each static method that explains what the method does.
• Indent all lines within a class by four spaces, and all lines within a method by four additional spaces.

Grading criteria for Part II

• 1 point for submitting a file with the correct name
• 5 points for comments and indenting (see above)
• 12 points for correct output — including the correct number of blank lines. All of these points will be lost if your program fails to compile.
• 12 points for taking full advantage of procedural decomposition.

Submitting your work for Part II

Submit your BlockLetterWriter.java file by taking the following steps:

1. Login to Gradescope by clicking the link in the left-hand navigation bar.

2. Click on the box for CSCI S-111.

3. Click on the name of the assignment in the list of assignments. You should see a pop-up window with a box labeled DRAG & DROP. (If you don’t see it, click the Submit or Resubmit button at the bottom of the page.)

4. Add your file to the box labeled DRAG & DROP. You can either drag and drop the file from its folder into the box, or you can click on the box itself and browse for the file.

5. Click the Upload button.

6. You should see a box saying that your submission was successful. Click the (x) button to close that box.

7. The Autograder will perform some tests on your file. Once it is done, check the results to ensure that the tests were passed. If one or more of the tests did not pass, the name of that test will be in red, and there should be a message describing the failure. Based on those messages, make any necessary changes. Feel free to ask a staff member for help.

   Note: You will not see a complete Autograder score when you submit. That is because additional tests will be run later, after the final deadline for the submission has passed. For such problems, it is important to realize that passing all of the initial tests does not necessarily mean that you will ultimately get full credit on the problem. You should always run your own tests to convince yourself that the logic of your solutions is correct.

8. If needed, use the Resubmit button at the bottom of the page to resubmit your work. Important: Every time that you make a submission, you should submit all of the files for that Gradescope assignment, even if some of them have not changed since your last submission.

9. Near the top of the page, click on the box labeled Code. Then click on the name of each file to view its contents. Check to make sure that you see the code that you want us to grade.

Last updated on June 24, 2025.