mersenneforum.org a partial sudoku puzzle
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2017-06-28, 14:43   #1
MattcAnderson

"Matthew Anderson"
Dec 2010
Oregon, USA

100100110112 Posts
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
 partial sudoku puzzle.pdf (198.3 KB, 155 views)

 2017-06-28, 15:14 #2 CRGreathouse     Aug 2006 176316 Posts 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.
2017-06-28, 21:14   #3
science_man_88

"Forget I exist"
Jul 2009
Dartmouth NS

2×3×23×61 Posts

Quote:
 Originally Posted by MattcAnderson 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:

$
\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}$

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

2017-06-28, 21:36   #4
chalsall
If I May

"Chris Halsall"
Sep 2002

251728 Posts

Quote:
 Originally Posted by science_man_88 ...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

 2017-06-29, 07:14 #5 MattcAnderson     "Matthew Anderson" Dec 2010 Oregon, USA 32·131 Posts 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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