Problem Set 4: Forensics


  1. Watch Week 4’s lecture.

  2. Figure out whodunit.

  3. Resize some images.

  4. Recover some photos.

  5. Submit your code.

  6. Submit a form.


For help with Week 4 and Problem Set 4:

  • Attend David’s and Rob’s walkthrough on Wed 9/28, 1pm – 2:30pm, in Sanders.

  • Watch Zamyla’s walkthroughs herein.

  • Attend your TF’s section (or another if you have a conflict).

  • Take advantage of help50, eprintf, and debug50.

  • Post questions and search answers in CS50 Discuss.

  • Attend individual TFs' and CAs' office hours at HSA.

  • Attend course-wide office hours:

    • Wed 9/28, 9pm – 11pm, Widener

    • Thu 9/29, 9pm – 11pm, Widener

    • Sun 10/2, 3pm – 5pm, atrium of Northwest Science

Getting Started

Alright, here we go again!

Log into and execute


within a terminal window to make sure your workspace is up-to-date.

Next, execute

mkdir ~/workspace/pset4/

at your prompt in order to make a directory called pset4 in your workspace directory.

Now execute

cd ~/workspace/pset4/

and your prompt should resemble the below.

~/workspace/pset4/ $

What to Do

  1. Implement Whodunit

  2. Implement either of:

  3. Implement Recover

Fabulous Prize

And now the real fun begins. You are hereby challenged to find as many of the computer scientists featured in the photos that you recovered for Recover as possible. To prove that you found someone, take a photo of yourself posing (anywhere) with the computer scientist (in such a way that he or she is aware of the photo and not just in the background). If a photo contains multiple computer scientists, you’re welcome to pose with each of them separately. Upload your photos (i.e., the photos you took, not the ones that you recovered) to a non-private album somewhere that supports bulk downloads (e.g., Dropbox, Imgur, etc.), then email your album’s URL to by noon on Mon 10/10! We’ll add your photos to a public gallery (unless you request otherwise).

Whoever finds and photographs the most computer scientists (and, in the event of a tie, submits first) shall be rewarded with a fabulous prize.

How to Submit

Step 1 of 2

  • Update your IDE:

  • Submit whodunit:

    cd ~/workspace/pset4/whodunit/
    submit50 whodunit
  • Submit resize:

    cd ~/workspace/pset4/resize/
    submit50 resize
  • Submit recover:

    cd ~/workspace/pset4/recover/
    submit50 recover

Step 2 of 2

This was Problem Set 4.