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July 6 puzzle

 
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pendrith



Joined: 07 Jul 2006
Posts: 3

PostPosted: Fri Jul 07, 2006 4:59 pm    Post subject: July 6 puzzle Reply with quote

I'm stuck on the July 6 puzzle. Can anyone explain the logic required to continue??

942---567
173562948
856-4-312
-29---673
78----25-
63--2-48-
3--28-79-
--8-7312-
2-7---836
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Fri Jul 07, 2006 6:11 pm    Post subject: Row on block interaction Reply with quote

To proceed you need to analyze where a "1" can fall in row 4.

-- There cannot be a "1" at r4c1 because of the "1" at r2c1.

-- Therefore the "1" in row 4 must fall in the middle center 3x3 box. This means that you can eliminate the possibility of a "1" in the rest of that box -- at r5c4-6, and at r6c4&6, in other words.

-- Now you can find a naked pair {7, 9} in column 4 -- at r3c4 & r6c4. So you can set r8c4 = 6, and the rest should be relatively straightforward. dcb
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pendrith



Joined: 07 Jul 2006
Posts: 3

PostPosted: Mon Jul 10, 2006 2:41 pm    Post subject: Reply with quote

Hi David

Thanks for responding.

I'm still confused however.

No doubt finding where the "1" falls in row 4 would help solve the puzzle.

I understand how there cannot be a "1" at r4c1

However I don't see how you can eliminate a "1" at r4c4 or r4c6

What am I missing??
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Marty R.



Joined: 12 Feb 2006
Posts: 5065
Location: Rochester, NY, USA

PostPosted: Mon Jul 10, 2006 3:58 pm    Post subject: Reply with quote

Quote:
However I don't see how you can eliminate a "1" at r4c4 or r4c6


I haven't yet done this puzzle and I'm not looking at any grid, but I'm not seeing where David said the "1" can be eliminated from those two cells.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Mon Jul 10, 2006 4:14 pm    Post subject: Reply with quote

942|xxx|567
173|562|948
856|x4x|312
-----------
x29|xxx|673
78x|xxx|25x
63x|x2x|48x
-----------
3xx|28x|79x
xx8|x73|12x
2x7|xxx|836

To repeat in other words, what David said:
In row 4 the 1 must be in column 4,5 or 6. So box 5 must have the 1 in this row and it cannot be elsewhere in that box (this is called box/box interaction, Locked Candidates 2 or Claiming). Therefore only 79 remain for r6c4, the same we have in r3c4.
Same thing for the 4: In row 9 the 4 must be in column 4 or 6. Therefore it cannot be in r7c6 or r8c4.
Looking at the remaining candidates in r8c4 now, it cannot be 4 and it cannot be 9 from the 79-pair in r36c4. Then only 6 is left.
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pendrith



Joined: 07 Jul 2006
Posts: 3

PostPosted: Mon Jul 10, 2006 6:31 pm    Post subject: Reply with quote

Got it!

Thanks guys
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sat Aug 19, 2006 11:23 pm    Post subject: Reply with quote

ravel wrote:
In row 4 the 1 must be in column 4,5 or 6. So box 5 must have the 1 in this row and it cannot be elsewhere in that box (this is called box/box interaction...)


I understand how this works, I just don't understand why it is called a box/box interaction. I quess I don't understand how a box could relate to another box except through a row or column and therefore why it wouldn't be a box/row interaction.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Sun Aug 20, 2006 11:48 am    Post subject: Reply with quote

I agree, that its not the best name (as for some other techniques). I suppose, it comes from the fact, that with a "box/line interaction" (locked candidates 1) you can eliminate candidates in the line (row/column), whereas with "box/box interaction" you can eliminate them in the box.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sun Aug 20, 2006 12:33 pm    Post subject: Reply with quote

Ravel,

Thanks. Your explanation was good enough to make the name seem logical.
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Sun Aug 20, 2006 12:58 pm    Post subject: block - block interactions Reply with quote

Here is another explanation:

http://www.sadmansoftware.com/sudoku/technique4.htm

I think most of us find these in the course of looking for line - box interactions.

Keith
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Sun Aug 20, 2006 3:32 pm    Post subject: Re: block - block interactions Reply with quote

Ah, you found the link ! And yes, i think, it is unusual to spot box/box in the desribed way. This made it hard to understand the name.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sun Aug 20, 2006 9:00 pm    Post subject: Reply with quote

The explanation on the Sadman site seems totally backward to me, although if one did manage to look at it that way, the name would make more sense.

If we can have umpteen UR's labeled Type 1, Type 2, etc... it seems we should be able to keep track of box/line Type 1 (locked candidates 1) and box/line Type 2 (locked candidates 2). Or maybe just box/line and line/box would work. Nah, too many people would think that was a mis-print. Maybe it's time to organize a Sudoku board of governours to standardize/logisize terminology.
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Mon Aug 21, 2006 1:04 am    Post subject: Standardize? Reply with quote

Tracy,

You are correct. I don't think a box-box interaction is something different to learn. I also did not understand the Sadman explanation when I originally found it. I thought I was stupidly missing something.

Also, I'd like to see more standard terminology. I tried to impose one on myself:

"Box" not "block" or "square"..
"Candidate" not "possibility".
(Box - Line) "Interaction" not "intersection".
"Line" not "row or column".
"Naked single" not "forced square".
"Cell" not "square".
"Hidden single" not "pinned square".

It's tougher than I thought, to consistently use one set of terms.

By the way, my wife's cousins were here from Kalamazoo for (a family reunion and) the Woodward Dream Cruise this weekend. In just a few years, the Cruise has become an incredible event and spectacle.

Best wishes,
Keith
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