With thanks to CS50’s alumni and friends

CS50 and Facebook present…

CS50 Puzzle Day 2020

CS50 Puzzle Day is over in all time zones! Like to attend walkthroughs of the solutions via Zoom or YouTube at ?

CS50 Puzzle Day 2020 is online-only. Team members should NOT gather in person, unless they already live together. All team members should instead collaborate online via chat, voice, or video. Doctors’ orders! Teams (whose members don’t live together) discovered to have gathered in person will be disqualified.

Table of Contents

What is CS50 Puzzle Day?

Solve a packet of problems!

CS50 Puzzle Day 2020 is an online adaptation of an event that we ordinarily hold in person at Harvard and Yale each September, an opportunity to collaborate on a team with classmates, family, and friends on a packet of puzzles (i.e., logic problems). Not only is this September’s event open to students at Harvard and Yale, it’s also open to everyone around the world (just like CS50x Puzzle Day was this past spring), whether taking CS50 or not!

No prior CS experience required. Teams of size 2, 3, or 4 are encouraged, or you can participate on your own. If collaborating on a team, you MUST collaborate online via chat, voice, or video (unless you already live together).

Starts anytime after 00:00 on Friday, 4 September 2020, in your own time zone. Ends anytime before 23:59 on Monday, 7 September 2020, in your own time zone.

Register officially at cs50.ly/register anytime before 23:59 on Monday, 7 September 2020. Every member of your team should register individually by submitting the form as well.

See medium.com/@cs50/this-was-cs50x-puzzle-day-2020-95176423293c for some past puzzles and solutions. Indeed, the best way to practice for this year is to solve past puzzles first!

How does it work?

Anytime after 00:00 on Friday, 4 September 2020 (in your own time zone), your team will download a packet of puzzles as a PDF. So long as it’s after 00:00 on Friday in at least one team member’s time zone, you may begin!

Your team will then have until 23:59 on Monday, 7 September 2020 (in your own time zone), to solve as many puzzles as you can. You’ll submit your answers online via a Google Form at cs50.ly/submit. So long as it’s before 23:59 on Monday in at least one team member’s time zone, you may still submit!

Take photos while you work on the puzzles (or screenshots of your team collaborating online)! We’ll then share them online if you’d like.

On , we’ll walk everyone through the (correct!) answers via Zoom. If unable to attend live, we’ll post a recording thereafter.

, we’ll walk everyone through the (correct!) answers via Zoom. If unable to attend live, we’ll post a recording thereafter. Puzzles will not require prior programming experience, just logic and smarts. All you’ll need is a computer with Internet access, a pen or pencil, and scratch paper.

What are the rules?

CS50 Puzzle Day 2020 is online-only. Team members should NOT gather in person, unless they already live together. All team members should instead collaborate online via chat, voice, or video. Doctors’ orders! Teams (whose members don’t live together) discovered to have gathered in person will be disqualified.

Teams of size 2, 3, or 4 are encouraged, but you may form larger teams of reasonable size. (You’ll declare your team when you submit your answers.) Consider, though, that the larger your team, the less each team member will be challenged by puzzles! Teams deemed by CS50’s staff to be of unreasonable size will be disqualified and ineligible for certificates.

Teams may not share hints or answers with other teams. Teams deemed by CS50’s staff to have shared hints or answers with other teams will be disqualified and ineligible for certificates.

What are the puzzles?

Here is a PDF of the packet of puzzles that you can download and/or print!

Packet of Puzzles

Quotes from last year!

“I met amazing people and I had so much fun. Thank you :)”

“my mind was blown away with these puzzles and i’m looking forward to it next year”

“Enjoyed it very much and fried my brain”

“This has been a lovely experience. Not only has it challenged me and everyone on my team, but it made me reach out to other people from different countries and get out of my comfort zone. I will definitely be doing this next year.”

“This is exceptionally good competition. I’m very greatful to organizers. I hope that people all around the world who were solving this puzzles are as happy as me.”

“The real answer was the friends we made along the way”

”[**] that was hard”

Photos (and memes)!

Do consider taking photos or screenshots of your team working on puzzles (or even creating CS50 Puzzle Day 2020-related memes), and submit them at cs50.ly/photos!

Here are photos and memes that have been submitted already!

Questions?

If you have a question about a puzzle, email puzzles@cs50.harvard.edu, and we’ll do our best to reply! Afraid, though, we won’t be able to offer any hints!

How to submit?

Submit your answers at cs50.ly/submit by 23:59:59 on Monday, 7 September 2020, in your own time zone!

Who are the winners?

CS50 certificates were awarded to any team that solved more than half (5 or more) of the puzzles!

See docs.google.com/spreadsheets/d/e/2PACX-1vQGwZLX6HaapK-HhfUOkO0XGGhy8cDnp9AR4TeSbTLeGptsUsA6rsWtRkS891eqxGgKEPmhGNf7AFT4/pubhtml?gid=632636133&single=true for all teams’ scores.

What were the right answers?

See video.cs50.io/-4OsBRuN1o0?start=77!

One error in the walkthrough for The Sound of Silence: there is a fifth word that gives you the five-letter answers, the statement about the silent H was incorrect.

Acknowledgements

Special thanks to CS50’s alumni and friends at Facebook for writing this year’s puzzles!