Sudoku constructor?

February 27, 2009 11:48 AM

Is there a program that will take an already solved sudoku and create a medium difficulty unsolved puzzle?

I'm making a word sudoku. You enter nine unique letters instead of numbers, and once it is solved, there is a word spelled out on the diagonal. I've worked out the solution to the puzzle, and would now like to make a playable board. Rather than randomly delete things and test its difficulty, I was hoping there might already be a tool out there that will take a solution and make a solvable puzzle out of it.

posted by team lowkey to technology (7 comments total)

If I understand you correctly and you're spelling out just one word, how about finding a medium sudoku and assigning letters to the numbers by following the diagonal on its solution?
posted by hydrophonic at 12:01 PM on February 27

Sorry, not just one word. Still, the diagonal has to match the pattern of the word, which in this case is 123451678, which would be kind of a drag to find a matching puzzle.

My puzzle also spells a pair of words across the top, so the top row has to be 196782435.

Those are the specific constraints, if someone knows any way to turn that into a puzzle.
posted by team lowkey at 12:16 PM on February 27

Something like this?

196782435
428135796
573649281
215493867
347856912
689271354
731528649
852964173
964317528

the puzzle for which is:

_9______5
4_81__7__
57__49___
___4__86_
_4__5__1_
_89__1___
___52__49
__2__41_3
9______2_

?

I used a thing called Sudoku Dragon to do that. The process is as follows:
1. Enter the constraints (the numbers you want).
2. Solve the puzzle to get the rest of the numbers.
3. Follow the instructions here, removing symmetrical pairs of numbers and checking for a unique solution.
posted by le morte de bea arthur at 12:38 PM on February 27

p.s. I didn't do a great job with that puzzle - with a bit of trial and error I'm sure you could remove a lot more of the numbers.
posted by le morte de bea arthur at 12:39 PM on February 27

I modified this sudoku puzzle's generator so that it always generates puzzles with the desired characterstic, then set it to Intermediate difficulty and generated several puzzles until there was one with few letters given on the diagonal or top row. I got this: puzzle and solution. contact by memail if you'd like another version---I can generate in any of 6 difficulties from "basic" to "unreasonable".
posted by jepler at 2:08 PM on February 27

That's awesome! Thanks! It might be a little too difficult for the audience, but it's easy to make it easier. But I'll probably just use it as is.

And le morte de bea arthur, those instructions are useful for any further puzzles I might try to create, so thanks for that, too.
posted by team lowkey at 3:45 PM on February 27

Interesting concept!

I came up with a similar idea for using a solved sudoku puzzle to create a secure password square that is constrained to have the same number of letters, numbers and symbols in each row, column or 3x3 square.

Here's the idea, if you're interested.
posted by Araucaria at 10:27 PM on February 27