This was CS50x Puzzle Day 2024

Yuliia Zhukovets, Carter Zenke, Doug Lloyd, David J. Malan

21 min readApr 9, 2024

And that concludes CS50x Puzzle Day 2024! This year’s event brought more than 10,000 of registrants from 164 counties together to participate in a “fun mental workout,” a quote from one of last year’s participants! We are excited to share what we learned from this year’s event and share with you some of the numbers, stories, photos, and more!

This year, we celebrated the ninth CS50x Puzzle Day! The tradition commenced in 2016, when we decided to make our on-campus CS50 Puzzle Day at Harvard (and Yale!) available to CS50x students around the world. In fact, CS50x Puzzle Day is not just a “day” but a long weekend and a bit of solving puzzles with friends, colleagues, and family. We indeed spread it over a weekend that starts when the first time zone on Earth enters Friday and when the last time zone on Earth exits Monday. That way, everyone has a weekend, as well as a couple weekdays, to embark on the “brain scratching joyride” at school, work, or home. And just about 5 days ago, at 00:00:00 on Friday, April 5, all the registrants were invited to download a packet of puzzles, written by CS50’s friends at Meta: Amy Qiu, Helen Chen, James Wu, Ryan Liu, Zach Zagorski, and more.


This year, 11,013 people registered for CS50x Puzzle Day 2024. We were delighted to welcome 7,959 who had never participated in CS50x Puzzle Day, 1,227 who had participated once before, 652 who had participated twice, and 855 who had participated three or more times. (A few participants didn’t answer the question, so their data isn’t reflected here.) And of course a very special group of 41 who stated they had participated in every prior CS50x Puzzle Day!

Among the registrants were:

  • 2,103 registrants from the United States
  • 1,610 registrants from India
  • 1,076 registrants from Iran
  • 666 registrants from Pakistan
  • 438 registrants from Canada
  • 382 registrants from the United Kingdom
  • 286 registrants from Ukraine
  • 276 registrants from Singapore
  • 270 registrants from Brazil
  • 192 registrants from Australia

Here’s a quick glance at how all teams scored this year. Each team that provided correct answers to a majority (at least five) of the nine puzzles was awarded a CS50x Puzzle Day 2024 certificate — if you’re among these teams, keep an eye out for an email from the CS50 Bot in the coming days! (Email if it doesn’t seem to arrive, but do check your spam folder first!)

Our Google Form tracked submissions from 1,815 teams and individuals (give or take!), and even more may have participated without ultimately submitting the solution form. Here’s a breakdown of how many teams scored correct answers on each puzzle:

Overall, about 435 teams correctly found the solutions to all puzzles, including the metapuzzle itself. 1,528 teams correctly solved at least one puzzle!

We also asked teams to characterize some of the puzzles; as you can see from the below, Books was deemed the favorite of the lot.

There was a similarly clear winner for the hardest puzzle, with MapGPT taking that award.

But an even clearer winner emerged for the easiest puzzle, with The Round of Music running away with it:


And here are the solutions themselves! Note that we accepted multiple solutions for some of the puzzles.

  • The Round of Music accepted MAYCOMB.
  • Zoo Pals Mystery Dinner accepted both SNOWPIERCER and WOUNDS.
  • Room Decor accepted both OPEN SHORTEST PATH FIRST and OSPF.
  • Roleplay accepted SERRANO.
  • Books will accepted both ORION and RIGEL.
  • MapGPT accepted ODYSSEY.
  • Connect Four accepted TITANIC.
  • Cycleword accepted GEORGE ORWELL.
  • A Haunting Conclusion accepted SPLIT THE RENT.

Not sure how to get to those answers? Check out the step-by-step walkthrough of puzzles below:

Playlist of solutions


Now a CS50x Puzzle Day tradition, memes expressed both frustration and joy.

Participants’ Reflections

Considering joining us next year? Here’s what a few participants had to say:

  • “I haven’t been so excited about something for a long time, it’s like a childlike joy!”
  • “Your brains will melt, in the best possible way!!”
  • “CS50x Puzzle Day was a terrific challenge. Frustrating at times, but when the answers came it was so satisfying. I loved it!”

Or, as one person put it more succinctly:

  • “Just do it”

Now to conclude, thank you to everyone around the world who took photos (and screenshots) of their teams solving puzzles!





Harvard University’s introduction to the intellectual enterprises of computer science and the art of programming.