This was CS50x Puzzle Day 2022

Carter Zenke and David J. Malan

7 min readApr 6, 2022

And we’re a wrap! As the clock strikes midnight in the last time zone on Earth, we can look back on CS50x Puzzle Day 2022. This year’s event brought thousands of registrants from 88 countries together to “enjoy not having a clue when you have a ton of ’em” (among our favorite quotes online!). We’re excited to reflect on all we’ve learned from this year’s event and to share some of the stories we’ve heard over the past few days!

This year is far from CS50x Puzzle Day’s first incarnation — it is, in fact, the sixth annual CS50x Puzzle Day! The first event commenced in 2016, when we decided to make our on-campus Puzzle Day at Harvard (and Yale!) available to CS50x students around the world. Calling CS50x Puzzle Day a “day” is something of a white lie: instead of confining the event to a few hours, we spread it over an entire 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 both a weekend and a couple weekdays to participate (e.g., at school or work). When all is said and done, that’s about five calendar days of puzzling! At 00:00:00 on Friday, 1 April 2022, students around the world were invited to download a packet of puzzles, written by our friends at Meta: Cameron Bates, James Wu, and Zach Zagorski.

As usual, we encouraged participants to form teams of 2–4. As COVID-19 restrictions ease in some parts of the world, some teams gathered in person while following their local health guidelines. 😷 Others chose to continue collaborating over the internet, using platforms like Zoom, WhatsApp, and Discord to connect across countries and time zones. Whether you gathered in-person or online, we were delighted to see teamwork alive and well in the world!


It’s hard to believe, but 12,051 people registered for CS50x Puzzle Day 2022. We welcomed 10,173 who had never participated in C50x Puzzle Day, 1,047 who had participated once before, 464 who had participated twice, and 344 who had participated three or more times. A small group of 31 had participated in every CS50x Puzzle Day!

Among the registrants were:

  • 2,710 registrants from India
  • 1,880 registrants from the United States
  • 1,151 registrants from Iran
  • 406 registrants from Canada
  • 379 registrants from the UK
  • 275 registrants from Singapore
  • 239 registrants from Nigeria
  • 201 registrants from Brazil
  • 200 registrants from Egypt
  • 185 registrants from Pakistan

We were especially happy to see 136 participants from Ukraine, all of whom have been in our thoughts these past several weeks.


Here’s 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 2022 certificate — if you’re among these teams, keep an eye out for an email from the CS50 Bot in the upcoming days! (Email if it doesn’t seem to arrive, but do check your spam folder first!)

Our Google Form tracked submissions from 1,459 teams and individuals, 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 100 teams correctly found all solutions to the puzzles, including the metapuzzle itself:

If we take a look at the individual puzzles themselves, we see that #4 was most widely regarded as the “easiest”, followed by If At First You Don’t Succeed. Note that “easiest” doesn’t necessarily mean “easy”!

Running away with the title of “hardest puzzle” was MAPS, with 330 votes, followed by Harry Potter and the Off-by-One Error, with 239 votes.

And among participants’ favorites were Puzzling Pyrotechnics and Portholes.


And here are the solutions themselves!


Now something of a CS50x Puzzle Day tradition, memes expressed both frustration and joy, particularly around this year’s metapuzzle!

By Chantal, Hans Husurianto, Jonathan Ho, Max DeMaio, Tewfik Ghariani, and Victor He.

Participants’ Reflections

As part of the submission form, we asked participants to share their thoughts on this year’s CS50x Puzzle Day. Happy to share that the results were quite positive, if not skewing a bit in the “hard” direction!

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

  • “You should join! It’s a very fun and thrilling, especially if you’re doing it with friends!”
  • “The best experience ever.”
  • “my brain is steaming”
  • “A fantastic challenge in creativity, and teamwork.”
  • “Do not worry if you do not find an answer, in the end, it brings a lot of laughter along with a brainstorming :)”

If teamwork, laughter, and brain steaming sound like your idea of fun, we hope to see you next year. Of course, if you do decide to join, you might find yourself among those leaving more succinct comments:

  • “It’s HARD!”

“Hard fun”, we might like to say :)

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

By Abdulazeez Oboh, Achint Raj, Agastya Dey, Alireza Mortezai, Amirah Natasha, Anant Dongre, Anthony Saab, Arpan Pandey, Brian Deng, Chinmay Kotkar, Danial Hadizadeh, Dev Kumar Thapa, Diya Parelkar, Giovanni Seiji, Eric Lin, Ida Zdanowicz, Julia Pich, Kireina Kameloeh Natalia Oryza Sativa Garang, Mahmoud Ramzi, Melissa O. Santañez, Melsen Carlsburg, Nathan Howes, Omama Khan, Parham Rezaei, Prayansh Sukhija, Qitian Ru, Ravi Srivastava, Reed Steinmetz, Sarakiel Rayco, Sepide, Stephen Sacchetti, Stewie, Team Brillemans, Toma Kabysh, Victor Aarão, Vincent, and Willian Wallace Pereira Diogo.




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