This was CS50x Puzzle Day 2023

Carter Zenke, Doug Lloyd, David J. Malan

19 min readApr 5, 2023

That’s all for this year! This year’s event brought together thousands of registrants from 156 countries. 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, we celebrate the eighth 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. Calling CS50x Puzzle Day a “day” is something of a misnomer: we instead 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 both a weekend, as well as a couple weekdays, to participate at home, school, or work. At 00:00:00 on Friday, March 31, 2023, students around the world were invited to download a packet of puzzles, written by our friends at Meta: Amy Qiu, Cameron Bates, James Wu, and Zach Zagorski:

We encouraged participants to form teams of 2–4, whether in-person or online. We were delighted to see teamwork alive and well in the world!


This year, 11,637 people registered for CS50x Puzzle Day 2023. We welcomed 7,627 who had never participated in CS50x Puzzle Day, 2,188 who had participated once before, 692 who had participated twice, and 828 who had participated three or more times. (A few participants didn’t answer the question, so their data isn’t reflected here.) A small group of 43 stated they had participated in every prior CS50x Puzzle Day!

Among the registrants were:

  • 2,210 registrants from the United States;
  • 2,027 registrants from India;
  • 829 registrants from Iran;
  • 489 registrants from Canada;
  • 456 registrants from the United Kingdom;
  • 405 registrants from Ukraine;
  • 199 registrants from Germany;
  • 185 registrants from Brazil;
  • 137 registrants from Australia; and
  • 119 registrants from Egypt.


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 2023 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 1,627 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 862 teams correctly found all solutions to the puzzles, including the metapuzzle itself, which is quite a bit more than usual. We suspect this is the result of this year’s system, which informed participants of whether answers were right, as well as the introduction of hints throughout the event. As in 2019, this year’s certificates thus acknowledge winners’ scores as being “among the highest,” rather than singling out teams who solved all 9 puzzles.

We also asked teams to characterize some of the puzzles; as you can see from the below, Pixelated was far-and-away deemed the easiest of the lot:

Though there was a bit more of a split on which might be considered the hardest, with Problematic and Metaverse Hospital basically tied for that award:

And perhaps showing that its viral status in 2022 was no fluke, Catewordle, a puzzle based on the popular word game, was deemed the favorite, with Game Room close behind!


And here are the solutions themselves!

Playlist of puzzle solutions

Souvenir Photo


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

See article’s end for all photo credits!

Participants’ Reflections

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

  • “Solving CS50’s puzzle is the definition of euphoria, the feeling when it clicks!”
  • “I love the way that the different styles of puzzles make me think in different ways. When I get tired of one, I just switch to another and keep going!”
  • “Anyone can do it and it is a lot of fun! Let’s team up next year! 😎”

Or, as one person put it more succinctly,

  • “my brain hurts but it was fun”

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

By Aditya Sood, Agastya Dey, Agustina Giacometti, Ajay Babu Subhash, Alex Liu, Alexey Berezovikov, Alireza Mortezai, Amirhossein Rahmati, Anastasha Rachel Gunawan, Anderson Duarte Medeiros, Andrew Matheu, Andrii, Anna, Ashish Thomas Varghese, Ashlee, Astala Abdenour, Audran Tiedang, Audran Wolfhards, Bahaa, Bhuvan Patel, Borna Rahmani, Carolina Moreira, Chaitanya Moreira, Claude Pascalmboum, Cristian Ibadango, Danh, Debarpita Das, Dev Kumar Thapa, Divyansh Sukhija, Dmytro Kalitin, Dongkwang Kim, Dylan Khoo, Eduardo Sanzio, Elitzur, Erfan Asgari, Eugene Yang, Faye Atendido, Fetchy, Frenki Muça, Gabrial Acassio Correia, Gulshan, Gustavo Kenzo Araki Takechi, Hamed, Heather, Hikmat Budha Chhetri, Iram Nida Khalid, Jamie Furlong, Jason Deng, Jeff Poole, Jenny Hui, Jing Jing, João, Jose Antonio Rocha, Julia Pich, Katy Unger, Kimberly, KittenGang, Leanne Bell, Leen, Lindsey Exon, Linh Nguyen, Mahan Raftarhamedani, Mahmoud Ramzi, Malina, Manan Vadodaria, Maria F. Villalba, Maria Haddad, Marnitch, Matias, Mattia Beccari, Mattrixx, Maura Osorio, Melike Yildiz Aktas, Melissa Ong Santañez, Minas Alvertis, Miraz J Naina, Mohammad Mahdi Mesbahi, Mohammed Habibur Rahman, Muhammed Zafar M M, Mykola, Nada, Neil Bryan Caranzo, Nguyen Huy Thai, Nikola Kostadinov, Nikunj Patel, Nour Kamal Al-Masri, Noureddin Etkaidek, Nushrath Nazeer, Nuttapat Pittayapongporn, Oleh Pynzar, Olha Ivanyk, Olha Kondratenko, Osorio, Phan Nguyen Tuan Anh, Phi Plomp, Pontus, Poorna, Prithwis Das, Raman, Reed Steinmetz, Ricard Antonetti, Ronny Wan, Rupert Webb, Saeed Nazir, Samantha Seah, Sarah & Jay, Sarah Tan, Sarra Bach Chaouch, Shihan Embuldeniya, Soroush Saki, Susan Carlsen, Susan Hayashi Alonso, Swavidiana Triswa Santi, Teekam Suthar, Terry B, Tewfik Ghariani, Thais, Thang, Tharun, Tom, Truly Clark, Tuyishime Jean Paul, Victo Aarão Lemes, Victor Aarão Lemes, Viktorija, Vincent, Vinuka Vilhan Fernandopulle, Vlad, Yves Desclercs, Zahidul Islam, Zaina Khan, Ольга




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