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 Number of grids 
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Posted on: Mon Jan 14, 2019 11:32 pm




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Joined: Sun Nov 03, 2013 10:28 pm
Post Number of grids
Just recently, someone offered me the following question:
How many ways are there to fill in a 4x4 calcudoku grid? That is: How many ways are there to fill in a 4x4 grid with the numbers 1 to 4, such that every row and column contain each number once (permutations are allowed)? What about 5x5 grids? Or n by n grids?
I'm quite confident I've found the answer for 4x4 grids, but it isn't very elegant and doesn't easily generalise to bigger grids. This leaves me to wonder if there are nice ways answer these questions. I haven't given it too much thought, but I certainly will.
So if anyone wants a puzzle, I challenge you to take a stab at this one [biggrin]


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Posted on: Tue Jan 15, 2019 8:03 am




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Joined: Sun Mar 11, 2012 8:48 pm
Post Re: Number of grids
My first impression is 288: 4! x 3! x 2! x 1!


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Posted on: Tue Jan 15, 2019 9:57 am




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Joined: Thu May 12, 2011 11:58 pm
Post Re: Number of grids
I've been thinking on and off about the question: how many possible 4x4 Calcudoku puzzles are there?

[blink]


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Posted on: Tue Jan 15, 2019 10:08 am




Posts: 456
Location: Dublin, Ireland
Joined: Tue Mar 01, 2016 10:03 pm
Post Re: Number of grids
While it's an interesting question, there's not a straightforward solution. If you look up Latin square on Wikipedia, you will find considerable detail on the mathematics. I'd post a link, but I don't know if that's permitted.


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Posted on: Tue Jan 15, 2019 10:12 am




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Joined: Thu May 12, 2011 11:58 pm
Post Re: Number of grids
paulv66 wrote:
While it's an interesting question, there's not a straightforward solution. If you look up Latin square on Wikipedia, you will find considerable detail on the mathematics. I'd post a link, but I don't know if that's permitted.

Fine to post a link of course [smile]


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Posted on: Tue Jan 15, 2019 11:11 am




Posts: 456
Location: Dublin, Ireland
Joined: Tue Mar 01, 2016 10:03 pm
Post Re: Number of grids
pnm wrote:
paulv66 wrote:
While it's an interesting question, there's not a straightforward solution. If you look up Latin square on Wikipedia, you will find considerable detail on the mathematics. I'd post a link, but I don't know if that's permitted.

Fine to post a link of course [smile]


Here you go - https://en.m.wikipedia.org/wiki/Latin_square


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Posted on: Tue Jan 15, 2019 2:15 pm




Posts: 245
Joined: Fri Jun 17, 2011 8:15 pm
Post Re: Number of grids
pnm wrote:
I've been thinking on and off about the question: how many possible 4x4 Calcudoku puzzles are there?

[blink]

That is an interesting question.

On top of the possible Latin squares are the possible cages overlaying the cells. Theoretically you can have 1 to 16 cages. And then each cage has an operation.

16 cages would mean each cage is a single cell and the operator is '=' for each cage.

A single cage including all 16 cells is possible, except two problems arise. First, - and / wouldn't work as operations. Second, neither +40 nor x331776 provide sufficient information for a unique solution.

And then there are a _lot_ of permutations in between.


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Posted on: Tue Jan 15, 2019 2:59 pm




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Joined: Thu May 12, 2011 11:58 pm
Post Re: Number of grids
First question would be how many possible puzzles there are
(and you'd like to correct for symmetries too I think)

Next is how many of these have a single solution..


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Posted on: Tue Jan 15, 2019 3:03 pm




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Joined: Sun Mar 11, 2012 8:48 pm
Post Re: Number of grids
Here is another link that shows how the answer to the number of 4x4 squares is determined

http://www.maths.qmul.ac.uk/~pjc/comb/ch6s.pdf


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Posted on: Tue Jan 15, 2019 9:51 pm




Posts: 614
Location: Ladysmith, BC, Canada
Joined: Fri May 13, 2011 1:37 am
Post Re: Number of grids
So, if you are talking about a 4x4 grid, does the total number of possibilities change when you "add" in the 4 different procedures??........not a Mathematician, but Iwouldn't think so??


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