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Don't understand hint logic
 
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PpPete



Joined: 28 Dec 2013
Messages: 1
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Background:
I posted a review on the Playstore that said
Contains some puzzles that cannot be solved by logic alone, sudoku should not need trial and error

and got response:
We assure you that every puzzle has a unique solution - one to be found with logic alone. There are NO unsolvable puzzles. If you come across a puzzle YOU deem unsolvable, feel free to post it to our forums (http://genina.com/forums/show/1.page) and we will show you how it is solved.


so I played a few games (Extreme) until I came to this one:
Based on the "assurance" that every puzzle can be found by logic I concluded that when I got stuck it must be me at fault so went for the "hint" option.
That - for no reason that I can understand - decided that in the cells I have put the "pencil marks" in red, the 4s and 6s could be dispensed with - and that "therefore" the 4 was to be found at the very head of that column.

Can anyone explain this to me?

jeka
(Forum Admin)



Joined: 12 Jul 2010
Messages: 242
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Look at the two cells that contain nothing but 4 and 6 in the center block (one cell above the 7 in the center and the other one below it). There you have two cells with the same set of two numbers (4 and 6) that belong in them. We don't know which cell will have which number, but we do know that between the two of them both 4 and 6 will be "spoken for" and so neither 4 nor 6 can be anywhere else in the same block.

That's why none of the cells you've marked with red pencil marks can contain 4 or 6. (This also means you can safely remove a 6 as an option for the center cell in the very last row, thus giving you another couple of cells to solve easily)

By the way, same would be true for 3 cells in the same block containing the same set of 3 numbers and so on.

Hope this helps.

This message was edited 1 time. Last update was at 30 Dec 2013 02:15:03

jeka
(Forum Admin)



Joined: 12 Jul 2010
Messages: 242
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Just to follow up, do you understand the logic now?
nfn



Joined: 3 Sep 2014
Messages: 2
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jeka wrote:
Just to follow up, do you understand the logic now?


Don`t know how about the topicaster, but I understand, thanks ))

What about this? Just hard level, but I can`t solved it I saw only one possible move:
jeka
(Forum Admin)



Joined: 12 Jul 2010
Messages: 242
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It is hard to tell with the settings you are using if you have made any entries or if this is the puzzle as given. Assuming what we see is the puzzle as given, there is already a 7 in the column you have marked (row 3, col 1). The 7 actually goes into the cell next to the one you have marked - column 2, row 9
nfn



Joined: 3 Sep 2014
Messages: 2
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Oh, sorry, of course 7 - column 2 row 9.

The puzzle as given.
jeka
(Forum Admin)



Joined: 12 Jul 2010
Messages: 242
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Let's look at row 2, column 1. The possible values are 3,4,8. See if you can eliminate any of them.
GreenLantern


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Joined: 28 Nov 2014
Messages: 4
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I realize this is an old post, but I just joined the forum. This is a basic pattern called Naked Pair.

The '4' and '6' in r46c5 form a naked pair and eliminate all 4's and 6's in Box 5 and column 5.

This message was edited 1 time. Last update was at 28 Nov 2014 06:00:04

 
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