CS50 Puzzle Day

Science & Engineering Complex
150 Western Ave, Allston MA 02134

Click to Register

3 hours of pizza, puzzles and prizes! Plus a free CS50 Puzzle Day t-shirt! đź‘•

CS50 Puzzle Day is an opportunity to collaborate on a team with classmates and friends on a packet of puzzles (i.e., logic problems). Among the event’s goals is to send a message that computer science is more about problem-solving than it is about, say, programming. Among the event’s other goals are prizes.

Teams of size 2, 3, and 4 allowed. Open to all Harvard students, whether taking CS50 or not.

Puzzles are not programming challenges. No prior CS or programming experience needed, just logic and smarts! See some past puzzles.

How to Get There

Science & Engineering Complex (SEC)
150 Western Ave, Allston MA 02134

Most folks tend to walk, bike, scoot, but there will also be some CS50-specific shuttles as follows!

  • 11:45am, 2 shuttles departing Quad for SEC
  • 11:45am, 1 shuttle departing Widener Library (on Mass Ave) for SEC


  • Grand Prize - Meta Quest 2, for one lucky raffle winner
  • 1st Prize - Portal Go, for each member of 1st-place team
  • 2nd Prize - Portal, for each member of 2nd-place team
  • 3rd Prize - Snack Magic, for each member of 3rd-place team

If multiple teams solve the same number of puzzles, ties will be broken based on who submitted first! CS50 staff eligible to compete for prizes but ineligible for raffle.

Past Photos

CS50 Puzzle Day 2019

CS50 Puzzle Day 2019

What to Bring

  • Laptop with charger
  • Pen/pencil
  • Scratch paper
  • Blanket or towel if you’d like such for sitting outside

How to Prepare

No preparation (or prior background or experience of any sort!) is expected. But you might find it helpful to peruse some past puzzles!

Past Puzzles

Here are (with a few tweaks since) Fall 2021’s puzzles and walkthroughs of solutions!

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.

Teammate Finder

Need a hand finding teammates? Add yourself to the spreadsheet at cs50.ly/teammates, keep an eye on it for others’ additions, and email anyone with whom you might like to form a team! A friendly “hey, like to work on a team together” email, with a little bit about yourself, should suffice to break the ice!

Past Quotes

  • A good activity to do with friends!
  • Difficult, Challenging, but most of all, Memorable!
  • Extremely fun but mind boggling at the same time
  • Great fun, and I think I even have a few non-grey hairs left!
  • Had the best online experience of my life. Got a chance to get to know many people from different countries. Absolutely loved the experience.
  • I can describe CS50 Puzzle Day in one word as Awesome. It’s just wonderful, I feel so confident after making new friends from other parts of the world, solving puzzles with them which improved my team coordinating skills. I have learned so much from the competition and my new friends and I would love to take part in this competition every year.
  • It was a lot of fun and a great way to use your mind in a different way than you usually do day to day.
  • It’s brainwreckingly good!


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