## Pi Day Sudoku

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In honor of Pi Day, Brainfreeze Puzzles (“we turn coffee into puzzles”) created a Pi Day Sudoku on a 12×12 grid.

The rules are a little different from standard Sudoku, in part because the blocks are jigsaw pieces rather than 3×3, and in part because the first 12 digits of π are used instead of the standard 1-9. Each row, each column, and each colored block (“jigsaw region”) contains the first 12 digits of pi

3 1 4 1 5 9 2 6 5 3 5 8

in some order. In particular, there are two 1s, one 2, two 3s, one 4, three 5s, one 6, no 7s one 8, and one 9.

As a bonus, on Brainfreeze’s Pi Day site there are instructions for how to (possibly) win an autographed book by completing the puzzle. Woo hoo!
The contest is over: you can find the solution here.

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### 35 Responses to “Pi Day Sudoku”

1. Happy Pi Day, 2008! « Let’s play math! Says:

[…] Pi Day Sudoku Or get the printable pdf version here. […]

2. BigH Says:

Please provide a correct solution to this challenging problem. I will repay with big happy nice pretty picture.

3. Ξ Says:

I don’t have one yet… (It’s a doozy, isn’t it?)

4. Rafia Says:

I have tried so many times but cannot figure out the middle part

5. rosemary Says:

I am trying but wonder if the puzzle isn’t wrong….anyone figure it out? HELP!!

6. Batman Says:

It is indeed solvable, but I found that the usual sudoku techniques don’t work.

7. klaus Says:

Rosemary,
the puzzle is consistent and has a unique solution. I found it and checked it. i was also tempted to think that it was wrong, because I first found an answer where every column, every region and all but two columns worked out. But i eventually realized where my mistake was.
The whole thing did take me roughly 6 hours, because of all the dead-ends.
If one sees all the leads right away, it could be done faster, but it is certainly a really difficult sudoko, certainly the hardest i have ever done.
my advice is to first do as much as you can with the 5’s. Then locate all the 4’s, then work on the 6’s, 8’s and 9’s, and then go back to the 5’s. The corner regions are also fairly easy to fill up. What makes the problem so hard is how little information you have on the 1’s and 3’s.

8. L Says:

9. Ξ Says:

I got it! Like Rafia, I had the most trouble with the middle part — with 35 squares left to go I hit a dead end. I ended up making a guess on one square and the rest fell into place; afterwards I went back and tried it with the other possibility for that square, and about halfway though filling in the rest got a contradiction. (I had lots of copies of the puzzle that I used in figuring this out). All told, I worked on this off and on throughout the day.

L, was this an assignment? I gave it to my students yesterday but didn’t actually require any of them to solve it! In deference to Brainfreeze Puzzles we can’t post the answers here on the site (because there’s a contest involved).

Edited 3/16 to add: I went back to look at my notes, and realized I didn’t need to guess after all: there was a column where any one of three squares could have been a 5, but I had overlooked that I needed three 5s. When I filled those in, the rest fell out easily. (I should have paid more attention to klaus’s words to start with the 5s!). So there is a unique solution, with no guessing required.

10. Stuck Says:

11. Stuck Says:

nevermind

12. Lucy Says:

13. Ξ Says:

Lucy, I started off the way I normally do with Sudoku (picking one of the digits that appears only once and looking row by row and column by column to see where that number might be). That worked to some extent — looking at the leftmost (or rightmost) 3 columns, there were only 4 jigsaw regions the digit could be in. This helped a bit, but not as much as usual.

Once I felt stuck, I made a note by each column and each row of what numbers were left to put in that column/row (including repetition, so a column might have 1 2 3 5 5 9 above it). And finally I went through cell by cell and wrote down what numbers could be in that cell. This was tedious, but turned out to be helpful — if there was only one cell in a row that could have a 2, then it must be a 2. Since the “legs” of the Pi symbol are only two columns wide, too, if a digit couldn’t be in one of those two columns it must be in the other, and that helped to eliminate possibilities for some of the cells that were above and below the “legs”.

(I also found this to be the most challenging puzzle I’d done — I’m certain that my approach wasn’t the most efficient, but in the end it did work.)

14. COCO Says:

I AM GOING CRAAAAZZZYYYYYYYYYY!!!!!!!!!!!!!!!!
I DON’T WANT ANY HINTS, I WANT THE ANSWERS!!!!!!!!!!!!!

15. COCO Says:

MY EYES ARE BLEEDING!!!!
I CAN’T TAKE THIS ANYMORE!!!

P.S. I REALLY NEED SOME EYEDROPS……….

16. BigH Says:

17. Ξ Says:

BrainfreezePuzzles.com created the Pi Day Sudoku and gave permission for it to be posted. However, they’ve requested that we not post the solution — I interpret that as also not posting a link to the solution.

I don’t, however, see any problem with posting suggestions for general approaches of how to solve puzzles like this (although that won’t help your bleeding eyes Coco!)

18. Batman Says:

We have chosen to respect the wishes of Brainfreeze and will not be posting any solutions, links to solutions, offers of email solutions, or anything else related to providing solutions to the puzzle. Any offers of solutions will be deleted from the comments.

19. Beasts Says:

I’ve been nibbling around the edges of this one for several days now, because I just can’t resist pi and a good sudoku puzzle. I had a Key Lime Pi Day, and coffee was eventually part of the solution, too. I’m now the proud owner of a contest entry form full of pi.

Hats off to Brainfreeze!

20. Brainfreeze Puzzles Says:

Oh, for shame, the students that want the answers so they can complete their assignment without doing the actual work! 🙂

The Pi Day Sudoku Contest from Brainfreeze Puzzles has come to an end. A solution will be posted at http://www.brainfreezepuzzles.com in a day or two.

-Laura

21. MathFest Sudoku! « 360 Says:

[…] The folk at Brainfreeze Puzzles (creator of the famous Pi Day Sudoku) have created a new puzzle for MathFest 2008 in Madison this […]

22. Printable Sudoku Puzzles Says:

This is going to be tough, going to have some time to kill in a couple of days, will definitely try this out. I wonder how many other kinds of sudokus are there.

23. Belcoris Says:

this looks like fun

24. bibek Says:

its so easy B-)

25. Pi Day Sudoku 2009 « 360 Says:

[…] Day Sudoku 2009 By Ξ Remember Pi Day Sudoku 2008?  Well the folk at Brainfreeze Puzzles have done it again!  Here’s their 2009 […]

26. Ikeiya Lynn Says:

i tried this puzzle. it is hard and confusing. i gve up and need the answers.:)

27. Ikeiya Lynn Says:

28. Ξ Says:

I thought this puzzle was a bit harder than the 2009 one. There’s a link at the very end of this post to the answers.

29. Beasts Says:

I felt it was harder than the 2009 Pi Day Puzzle, also. I think I’ve learned a few things in the year since this puzzle was published, but think the 2009 puzzle just might have been made a slight bit easier to encourage more entries.

There were not as many correct entries as I thought there would be, but hopefully the 2009 puzzle will have a few times more entries than this one. That would mean odds of winning would be reduced, but I already have the prized book. I’m already looking forward to Pi Day 2010!

30. Pi Day Sudoku Is Back! « 360 Says:

[…] Pi Day Sudoku Is Back! By Batman You laughed in 2008. […]

31. Pi Day « Para mis alumnos Says:

[…] is a special Sudoku , not very easy, with the first twelve digits of pi. And finally, let’s listen to this Pi […]

32. Pi Day Activities for Your Classroom - RenWeb Says:

[…] For more advanced students, here is a Pi Day Sudoku puzzle. […]

33. 15 Fun Pi Day Activities for Kids - SoCal Field Trips Says:

[…] 15. 360 – Pi Day Sudoku […]

34. Pi Day Party Resource Round-up – Humility and Doxology Says:

[…] Do you have a puzzle-lover?  Try this Pi Sudoku puzzle. […]

35. Pi Day Party Resource Round-up - Humility and Doxology Says:

[…] Do you have a puzzle-lover?  Try this Pi Sudoku puzzle. […]