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Homework 1: Setup

In CS 61B, we write code using real-world industry tools, and you’ll install those tools in this assignment.

Tools Overview: Terminal

There’s nothing to do in this section; you just need to read through it carefully. The actual tasks start at Task 1.

In CS 61B, we will use the terminal to run various commands.

When you work in a terminal, the terminal always has a working directory, which is the folder that the terminal is currently thinking about.

• The ls command lists all of the files in the working directory.
• The pwd command prints out the working directory.
• The cd command changes the working directory.

Many terminal commands behave differently depending on your working directory, so it is very important to ensure you are in the correct working directory before running a command! Remember, you can use pwd to check the working directory.

Further reading: Terminal guide

Tools Overview: Git

There’s nothing to do in this section; you just need to read through it carefully. The actual tasks start at Task 1.

Almost all computer scientists use Git when writing code. Git lets you take snapshots of different versions of your code (useful if you want to revert to an earlier version). Here’s a demo video:

Git also lets you sync a repository (a folder containing your code) on different computers. For example, you and your partner will use Git in later projects to work together.

One common place to sync code is GitHub. You can think of GitHub as a really big computer on the cloud, and everybody can sync their code to this computer (e.g. to save a backup copy, or to share the code with the world).

Git is very complicated, but there are a few core commands you should know for CS 61B.

• To copy a repo from GitHub to your computer (creating a new folder on your computer), use this command:

  git clone git@github.com:oski/name-of-oskis-repo.git
  

• To sync code from a repo on your computer, to a repo on GitHub, use these three commands:

  # First, take a snapshot of your code. (The commit message is mandatory!)
  git add .
  git commit -m "your commit message here"
  
  # Then, send your snapshot from your computer to GitHub.
  git push origin main
  

• To retrieve updates from a repo on GitHub, to a repo on your computer, use this command:

  git pull skeleton main
  

This diagram shows the repositories we use in CS 61B, and the commands you can use to sync code between them. (Click to enlarge.)

Further reading: Git guide

That’s it for the overview. Now, let’s start setting up your computer!

• If something isn’t working, do not try random things you find online. Ask a TA for help.
• Everyone should complete this lab on their own computer (no partners).
• Do not skip steps, or else you will run into errors later.

Task 1: Install Git

Click your operating system to see instructions.

macOS

1. Ensure that you have at least 40 GB of free space left on your disk.

2. Open a terminal. (⌘+spacebar, type “Terminal”, press Enter.)

3. In the terminal, run:

    xcode-select --install
   

   This might take some time.

   If you see “Command line tools are already installed,” move on to the next step (and make sure you see the version number in the next step).

4. In the terminal, run:

    git --version
   

   You should see a version number like git version 2.51.0 (a different number is fine) and no errors.

Windows

1. Head to https://git-scm.com/downloads/win and download the Git for Windows installer.

   

2. Run the installer. You’ll be faced with many options.

   We’ll only be selecting different options on the Select Components page, where we add a Git bash profile to the windows terminal.

   

   All the other options should be left as is. The entire install process is shown in the gif below:

   

3. Open a terminal. (Search for “Terminal” in the Start Menu.) We want Terminal, not Command Prompt.

   

   Older Windows versions may not have the Terminal app pre-installed. If you can’t find Terminal, install it from the Microsoft Store.

4. In the terminal, click on the drop-down arrow next to the plus “+” sign at the top and open the settings page.

   

5. Set the default profile to Git Bash, default terminal application to windows terminal and hit save.

   

6. Close the terminal, and open a new terminal. Your terminal should now look like this:

   

Linux

1. Use your package manager to install tools. If you’re on Ubuntu, run:

    sudo apt install git curl
   

   For other Linux distributions, you might need to replace apt install with yum install or something else.

2. In the terminal, run:

    git --version
   

   You should see a version number like git version 2.51.0 (a different number is fine) and no errors.

Task 2: Create GitHub repository

1. Create an account on https://github.com.

   If you already have an account, you do not need to create a new one.

2. Go to https://beacon.datastructur.es and follow the steps.

3. After completing all of the steps, you should receive an email invitation. Accept the invitation.

   This email will be sent to the email that you used to create your GitHub account, which may not necessarily be your Berkeley email.

4. After accepting, you should now have a GitHub repository at https://github.com/Berkeley-CS61B-Student/fa25-s12345 (instead of 12345, you will see a number unique to you).

   If you do not see a number (e.g. it says None), please click the Redo Registration button. If that fails, please make a post on Ed.

Task 3: Set Up Git

1. Open a terminal.

2. In the terminal, run these 2 commands. Replace oski and oski@berkeley.edu with your name and your email.

    git config --global user.name "oski"
    git config --global user.email "oski@berkeley.edu"
   

3. Run these 3 commands:

    git config --global init.defaultBranch main
    git config --global pull.rebase false
    git config --global core.editor "nano -w"
   

Task 4: Authenticate to GitHub

1. Open a terminal (or keep using the terminal you have open from previous tasks).

2. Run this command:

    curl -sS --ssl-no-revoke https://fa25.datastructur.es/assets/homeworks/hw01/get-ssh-key.sh | bash 
   

   In the output, you should see a line similar to one of these:

    Great! Your new SSH key is at: ~/.ssh/id_ed25519.pub
    You already have an SSH key at: ~/.ssh/id_ed25519.pub
   

3. Run this command. If your key is different from the lines above, replace ~/.ssh/id_ed25519.pub with the key you saw in your output.

    cat ~/.ssh/id_ed25519.pub
   

   You should see output similar to this:

    ssh-ed25519 AAAAC3NzaC1lZDI1N6jpH3Bnbebi7Xz7wMr20LxZCKi3U8UQTE5AAAAIBTc2HwlbOi8T oski@oski
   

4. Copy the output from the previous step.

   Go to GitHub’s SSH settings page and paste the output in the Key box.

   The title can be anything you want (e.g. “Laptop” or “Desktop” if you have multiple computers). Leave “Key type” as “Authentication Key.” Click “Add SSH key” to add the key.

   If you are retaking the class, you might see “Key is already in use.” If so, move on to the next step (and make sure you see the success message in the next step).

5. Back in your terminal, run this command:

    ssh -T git@github.com
   

   If the system asks “The key is not know by any other names. Are you sure you want to continue connecting (yes/no/[fingerprint])?”, type “yes”.

   If you see output like this, you’re done with this step:

    Hi USERNAME! You've successfully authenticated, but GitHub does not provide shell access.
   

   If you don’t see this output, redo the steps in this section. If it still doesn’t work after redoing the steps, ask TAs for help.

Task 5: Cloning Repositories

When you work in a terminal, the terminal always has a working directory, which is the folder that the terminal is currently thinking about.

• The cd command can be used to change the working directory.
• The pwd command can be used to print out the working directory.

Many terminal commands behave differently depending on your working directory. In this task, it is very important to ensure you are in the correct working directory before running a command.

For example, the command touch potato.txt creates a new file potato.txt in the working directory. If you run this command while in the wrong directory, you’d create the file in the wrong folder!

1. Open a file explorer (e.g. Finder on macOS) and create an empty folder named cs61b. This is where all your code will live.

   The cs61b folder can live anywhere, but we recommend putting it on your Desktop so that you don’t lose it.

2. Open a terminal. Use the cd command to navigate to your cs61b folder. For example:

    cd ~/Desktop/cs61b
   

   If you’re not sure how to use cd, read this terminal guide.

3. Run this command:

    pwd
   

   The output should end in cs61b (e.g. /home/oski/Desktop/cs61b). This means that your terminal’s working directory is the cs61b folder.

4. In the same terminal, run these 2 commands:

    pwd   # make sure this outputs a path ending in cs61b
    git clone git@github.com:Berkeley-CS61B/library-fa25.git
   

   If the command worked, your cs61b folder should now have a sub-folder named library-fa25 in it. You can check this by running ls in the terminal, or opening a file explorer.

5. In the same terminal, run this command:

    ls library-fa25
   

   This command lists the content of the library-fa25 folder. The output should have some lines like this:

    algs4.jar
    animated-gif-lib-1.4.jar
    antlr4-runtime-4.11.1.jar
    apiguardian-api-1.1.2.jar
   

6. In the same terminal, run these 2 commands, replacing 12345 with your repository number (from Task 2):

    pwd   # make sure this outputs a path ending in cs61b
    git clone git@github.com:Berkeley-CS61B-Student/fa25-s12345.git
   

   If the command worked, your cs61b folder should now have a sub-folder named something like fa25-s12345. You can check this by running ls in the terminal, or opening a file explorer.

   Do not run a git clone command multiple times. It will create multiple copies of the same folder on your computer, and this will cause trouble later.

   If you think you messed up this step, use a file explorer to search for folders on your computer named fa25-s12345. You should only have a single one!

   If you see a message like “warning: You appear to have cloned an empty repository,” it is safe to ignore.

7. In the same terminal (with pwd outputting ...cs61b), change the working directory to your folder, replacing 12345 accordingly:

    cd fa25-s12345
   

8. Run this command:

    git remote add skeleton git@github.com:Berkeley-CS61B/skeleton-fa25.git
   

   If you see a message like “fatal: not a git repository,” make sure you did the previous step.

9. Run this command:

    git remote -v
   

   Make sure you see 4 lines of output like this:

    origin      git@github.com:Berkeley-CS61B-Student/fa25-s12345.git (fetch)
    origin      git@github.com:Berkeley-CS61B-Student/fa25-s12345.git (push)
    skeleton    git@github.com:Berkeley-CS61B/skeleton-fa25.git (fetch)
    skeleton    git@github.com:Berkeley-CS61B/skeleton-fa25.git (push)
   

10. Run this command:

     git pull skeleton main
    

    If the command worked, your fa25-s12345 folder should now have a sub-folder named hw01 in it. You can check this by running ls in the terminal, or opening a file explorer.

    If you see “fatal: refusing to merge unrelated histories,” try running git pull skeleton main --allow-unrelated-histories --no-rebase instead.

11. Run this command:

     git branch -M main
    

12. At this point, your cs61b folder should have the structure below. Use ls in the terminal` or a file explorer to ensure your folder structure matches.

     cs61b
     ├── library-fa25
     │   ├── algs4.jar
     │   ├── animated-gif-lib-1.4.jar
     │   ├── antlr4-runtime-4.11.1.jar
     │   ├── apiguardian-api-1.1.2.jar
     │   └── ...
     ├── fa25-s12345
     │   ├── hw01
     │   │   ├── src
     │   │   │   └── Arithmetic.java
     │   │   ├── tests
     │   │   │   └── ArithmeticTest.java
    

Task 6: Set up IntelliJ

1. Ensure that you have at least 4 GB of free space left on your disk.

   Also, ensure you have at least 2 GB of free RAM (i.e. close other programs you don’t need).

2. Go to the JetBrains website and download and install the Community Edition (not the Ultimate version) of IntelliJ.

   You have to scroll down to find the Community Edition.

   

   For macOS users: If you have an M1, M2, M3 Mac, select “.dmg (Apple Silicon).” Otherwise, select “.dmg (Intel).”

3. Open IntelliJ. In the Welcome window, click the “Plugins” button in the menu on the left.

   On the window that appears, click “Marketplace” and enter “CS 61B” in the search bar at the top. The CS 61B plugin entry should appear.

   

   If you have the plugin installed from a prior term, make sure to update it.

4. Search for “Java Visualizer”, and click the green Install button to install the plugin.

   

5. Restart (quit and reopen) IntelliJ.

Task 7: Install Java

1. Open IntelliJ. If you have no projects open, click the “Open” button. If you have a project currently open, navigate to “File –> Open”.

   

2. Choose the hw01 directory inside your cs61b/fa25-s12345 folder.

   Do not choose the entire fa25-12345 folder. We want the hw01 sub-folder specifically.

   

3. Click “File” in the top-left of IntelliJ. In the drop-down menu, select “Project Structure” menu. Make sure you are in the Project tab. Click the SDK drop-down.

   If you see 21 in the SDK drop-down, simply select 21.

   If you do not see 21 in the SDK drop-down, click “Download JDK” to download Microsoft OpenJDK 21.

   

   

4. Make sure the “SDK” is 21 and the “Language Level” is “SDK default,” and press “OK.”

   

5. Close IntelliJ.

Task 8: Write code in IntelliJ

1. Open IntelliJ. Follow the “Opening in IntelliJ” steps in the Assignment Workflow guide.

   For the rest of the semester, every time you open an assignment, you have to follow those steps again. (Sorry, we know it’s tedious.)

   

   

   

2. You should now see the Arithmetic and ArithmeticTest files in the IntelliJ sidebar.

   

3. To test if everything is working correctly, run the Arithmetic class by clicking either the green triangle next to Line 6, or the green triangle in the top-right.

   

   If you get an error like package edu.princeton.cs.algs4 does not exist, make sure you followed the Assignment Workflow Guide in Step 1 of this task!

4. You should see a console pop up, prompting you to enter a number:

   

   If you follow the prompts, you will probably see that the math is wrong! Don’t fix it yet.

5. Open ArithmeticTest, and click either the green triangles next to public class ArithmeticTest, or the green triangle in the top-right. This runs the tests:

   

   

   We can see that “Test product correctness” passed, but “Test sum correctness” failed.

6. Edit the code in Arithmetic.java so that the tests pass. When you’re done, run the tests again and make sure they pass.

Task 9: Submitting your work

1. Open a terminal, and use cd to navigate to your fa25-s12345 folder.

2. Run this command:

    git status
   

   The output will tell you if you have any unsynced changes:

   

   This means your edit to Arithmetic.java is on your local computer, but not on GitHub.

3. Run these commands to sync your changes from your local computer to GitHub.

    git add hw01/src/Arithmetic.java
    git commit -m "fixed Arithmetic.java in hw01"
    git push origin main
   

   For future assignments, you can replace hw01/src/Arithmetic.java in the first command to add other files. You can also replace the message in quotes in the second command to describe your changes.

4. You can now run git status again, and it should say “Your branch is up to date with ‘origin/main.’” This means your changes are synced.

   You can also open https://github.com/Berkeley-CS61B-Student/fa25-s12345, and you should see your changes synced on GitHub!

5. Open https://gradescope.com, click on CS 61B, and click on the Homework 1 assignment.

   Select GitHub, then your fa25-s12345 repository and the main branch, and submit your assignment.

   If you don’t see the repository, you may need to link your GitHub account to Gradescope.

6. Once you submit, check that you’ve received full points on Gradescope.

   Congratulations on finishing the homework!

Appendix: Common Issues

Q: How do I set up a second computer or a new computer?

Setting up a second computer requires redoing Tasks 1, 3, 4, 5, 6, 7 on your second computer.

You would need to keep the two repos on the two computers in sync by running git push origin main on computer 1 (to send updates from computer 1 to GitHub), and git pull origin main on computer 2 (to download the updates from GitHub).