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Old 2017-06-28, 14:43   #1
MattcAnderson
 
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"Matthew Anderson"
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Default a partial sudoku puzzle

Hi MersenneForum,

I picked up a Sudoku book today and tried again at a puzzle that had stumped me before. I was able to put in the number 8 near the center and then I was again stumped.

I know there are some advanced Sudoku techniques out there, on the internet. Can anyone tell me a next step ( with logic) for the attached puzzle?

Also the possibility of a machine solver has been considered. This is from the "New York Post Bloom Sudoku Book" (fiendish puzzles c 2013). I am stuck on page 31.

I do not want to 'reverse engineer' the puzzle by looking in the answer section.

Regards,
Matt
Attached Files
File Type: pdf partial sudoku puzzle.pdf (198.3 KB, 76 views)
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Old 2017-06-28, 15:14   #2
CRGreathouse
 
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Well, in the top-right box you can fill in a 6 (in the bottom-middle position) because nothing else in the middle column can be a 6. Similarly the middle row across the top has only one position to put a 9, the middle of the left grid. That forces the "49" at the bottom to 4 and the "47" above it to 7, and probably cascades further.
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Old 2017-06-28, 21:14   #3
science_man_88
 
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Quote:
Originally Posted by MattcAnderson View Post
Hi MersenneForum,

I picked up a Sudoku book today and tried again at a puzzle that had stumped me before. I was able to put in the number 8 near the center and then I was again stumped.

I know there are some advanced Sudoku techniques out there, on the internet. Can anyone tell me a next step ( with logic) for the attached puzzle?

Also the possibility of a machine solver has been considered. This is from the "New York Post Bloom Sudoku Book" (fiendish puzzles c 2013). I am stuck on page 31.

I do not want to 'reverse engineer' the puzzle by looking in the answer section.

Regards,
Matt

Lets rewrite it here, on the forum ( in roughly,original form), instead of the file and rotating it:

<br />
\begin{tabular}{|c|c|c|c|c|c|c|c|c|}<br />
\hline<br />
&&6&&&&&9\\ \hline<br />
&&2&8&&6&&&1\\ \hline<br />
8&1&&&5&&&&\\ \hline<br />
&5&&&2&&&&\\ \hline<br />
&&3&7&6&1&9&&\\ \hline<br />
&8&&&3&&&1&\\ \hline<br />
&&&&9&&&4&3\\ \hline<br />
&&&3&&7&6&&\\ \hline<br />
2&&&&&&1&&\\ \hline<br />
\end{tabular}

now it's mostly a combination of set union, and set difference to consider.

Last fiddled with by science_man_88 on 2017-06-28 at 21:27
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Old 2017-06-28, 21:36   #4
chalsall
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"Chris Halsall"
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Quote:
Originally Posted by science_man_88 View Post
...now it's mostly a combination of set union, and set difference to consider.
Indeed. This puzzle is trivial to solve.

"2" is the only possible solution for 2x,5y. Everything simply cascades.

Last fiddled with by chalsall on 2017-06-28 at 21:43
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Old 2017-06-29, 07:14   #5
MattcAnderson
 
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"Matthew Anderson"
Dec 2010
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Smile thanks

Hi Mersenne Forum,


Thank you to all the responses to this thread.
I see Greathouse's reasoning for a 6 in the bottom row of the top right 3 by 3 grid.


Now this one should be easy.


Regards,
Matt
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