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-   -   a partial sudoku puzzle (https://www.mersenneforum.org/showthread.php?t=22422)

MattcAnderson 2017-06-28 14:43

a partial sudoku puzzle
 
1 Attachment(s)
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

CRGreathouse 2017-06-28 15:14

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.

science_man_88 2017-06-28 21:14

[QUOTE=MattcAnderson;462278]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[/QUOTE]


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

[TEX]
\begin{tabular}{|c|c|c|c|c|c|c|c|c|}
\hline
&&6&&&&&9\\ \hline
&&2&8&&6&&&1\\ \hline
8&1&&&5&&&&\\ \hline
&5&&&2&&&&\\ \hline
&&3&7&6&1&9&&\\ \hline
&8&&&3&&&1&\\ \hline
&&&&9&&&4&3\\ \hline
&&&3&&7&6&&\\ \hline
2&&&&&&1&&\\ \hline
\end{tabular}[/TEX]

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

chalsall 2017-06-28 21:36

[QUOTE=science_man_88;462313]...now it's mostly a combination of set union, and set difference to consider.[/QUOTE]

Indeed. This puzzle is trivial to solve.

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

MattcAnderson 2017-06-29 07:14

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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