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oct 3 vh

 
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Wed Oct 03, 2007 6:34 am    Post subject: oct 3 vh Reply with quote

so many cells with {1,8} ... calls for a w-wing:

one of r5c2 and r6c4 must be 8,
(connected by: 52( 18 )-42( 18 )-48( 28 )-66( 18 )-64( 18 ) )
so remove 8 from r5c5 and get naked pair 12 in box 5, thus r6c4=8

Later, remove 3 from r8c3 by this chain:

85-94=97-78=18-14=25-85

and the puzze is solved.

I am sure there were many more wings ...
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK

PostPosted: Wed Oct 03, 2007 11:49 am    Post subject: Reply with quote

Code:

+---------+-----------+---------+
| 4 5  2  | 136 8  16 | 7  36 9 |
| 8 6  7  | 9   23 24 | 34 1  5 |
| 9 3  1  | 46  7  5  | 8  46 2 |
+---------+-----------+---------+
| 3 18 9  | 7   4  12 | 5  28 6 |
| 7 18 6  | 5   12 3  | 9  28 4 |
| 2 4  5  | 8   6  9  | 1  7  3 |
+---------+-----------+---------+
| 5 7  34 | 2   9  8  | 6  34 1 |
| 6 9  34 | 134 13 7  | 2  5  8 |
| 1 2  8  | 346 5  46 | 34 9  7 |
+---------+-----------+---------+

Play this puzzle online at the Daily Sudoku site

Before reaching the above the XY wings using numbers 1 2 and 8 in boxes 5 and 6 sorted out the 8 in boxes 5 and 3 fairly directly

However I got to this point and once again used a "politically incorrect" logic
IF r8c4 is 4 then r3c4 = 6 and r1c6 is 1 and col 4 is denied room for 1. therefore r8c4 cannot be 4 so r9c7 is 3....
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Wed Oct 03, 2007 12:19 pm    Post subject: Reply with quote

I reached a very similar position, I guess, and also had to resort to "non-PC" logic:

Code:

+---------+-----------+---------+
| 4 5  2  | 136 8  16 | 7  36 9 |
| 8 6  7  | 9   23 24 | 34 1  5 |
| 9 3  1  | 46  7  5  | 8  46 2 |
+---------+-----------+---------+
| 3 18 9  | 7   4  12 | 5  28 6 |
| 7 18 6  | 5   12 3  | 9  28 4 |
| 2 4  5  | 8   6  9  | 1  7  3 |
+---------+-----------+---------+
| 5 7  34 | 2   9  8  | 6  34 1 |
| 6 9  34 | 134 13 7  | 2  5  8 |
| 1 2  8  | 346 5  46 | 34 9  7 |
+---------+-----------+---------+

Play this puzzle online at the Daily Sudoku site

I worked out, based on the 46 at R9C6 if you like, that either R9C4 or R1C8 must be 6 and therefore eliminated the 6 at R1C4. This finished it off, but I am curious whether there is a more standard logic available.

Peter

P.S. I see now it's exactly the same position as George's - sorry!
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Johan



Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium

PostPosted: Wed Oct 03, 2007 1:26 pm    Post subject: Reply with quote

Quote:

I am curious whether there is a more standard logic available.


Peter,

There is an x-wing in the grid that opens up an xyz-wing
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Wed Oct 03, 2007 2:04 pm    Post subject: Reply with quote

Oh, I had in fact seen the X-wing on 4's but still needed the logic I mentioned. I shall look if I can find the XY-wing.

Peter
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TexCat



Joined: 07 Jul 2006
Posts: 32

PostPosted: Wed Oct 03, 2007 2:06 pm    Post subject: Reply with quote

I used a skyscraper of 3's. Or perhaps it was several skyscrapers of 3's. : - )
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS

PostPosted: Wed Oct 03, 2007 2:18 pm    Post subject: Oct 3 Vh Reply with quote

An x-wing to eliminate a 4, an x-y wing to eliminate a 1, and an xyz-wing to eliminate a 6, and I was home.

Earl
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sheryl



Joined: 24 Sep 2007
Posts: 64
Location: New York

PostPosted: Wed Oct 03, 2007 2:47 pm    Post subject: 10/3 puzzle Reply with quote

can you please explain what this chain is?

Later, remove 3 from r8c3 by this chain:

85-94=97-78=18-14=25-85

can you explain what it is you are doing here. i'm down to these last few numbers and cannot find a way to eliminate them. i'm fairly new and i don't know what a wing is.

thanks.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Wed Oct 03, 2007 3:51 pm    Post subject: Reply with quote

sure I'll explain.

the numbers in the chain are coordinates of cells containing 3, "85" means r8c5.

an equal sign (=) means there are exactly 2 such cells in the unit that both cells share (94=97 means there is a 3 in row 9 in exactly two columns 4 and 7. The implication of this "strong link" being that if one cell is NOT 3, then the other is).

a dash (-) means the two cells share a unit (implication of this "weak link": if one cell is 3, the other cannot be 3)

the whole chain then reads like this: if r8c5 is 3 then r9c4 cannot be 3 then .. r8c5 is NOT 3. A contradiction, therefore r8c5 cannot be 3.

And of course there's a typo in my post: 3 is removed from r8c5 not r8c3

In practice I usually draw little diagrams of dots (one for each digit) and only connect the strong links. The chains are very easy to spot in these diagrams (see picture here:)


http://www.pictureupload.de/pictures/031007181032_Image014.gif

You'll find this technique under "x-chain" in sudopedia:
http://www.sudopedia.org/wiki/X-Chain
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sheryl



Joined: 24 Sep 2007
Posts: 64
Location: New York

PostPosted: Wed Oct 03, 2007 4:41 pm    Post subject: 10/3 puzzle Reply with quote

i wish i could say i understand, but i really am not getting it.


the whole chain then reads like this: if r8c5 is 3 then r9c4 cannot be 3 then .. r8c5 is NOT 3. A contradiction, therefore r8c5 cannot be 3.

i don't understand how you cme to the conclusion that 85 is not a 3. why can't 85 be a 3 and 94 not be the 3?

i think if i understood that it might help. i've looked at your diagram which i don't understand and i've looked at sudopedia but following the logic without understanding the terms yet is a bit difficult.

if you think i'm asking too much, i will understand. i appreciate your trying to help. thanks.
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duffy



Joined: 13 Sep 2007
Posts: 26
Location: Toronto Canada

PostPosted: Wed Oct 03, 2007 5:42 pm    Post subject: Reply with quote

Sheryl,
I like x-, xy- and xyz-wings, but they can be relatively difficult to spot: it is worth reading up on them. (Chains and W-wings are not part of my normal pencil and paper approach.) In this case, I probably did what Earl did. Maybe the following grid will help illustrate the use of these wings in this particular puzzle.
Code:

+---------+-------------+-----------+
|         | 136xyz   16 |           |
|         |          24x| 34x       |
|         | 4-6         |           |
+---------+-------------+-----------+
|         |          12 |    28xy   |
|         |             |           |
|         | -18         | 18        |
+---------+-------------+-----------+
|         |             |           |
|         |             |           |
|         | -4;36    46x| 34x       |
+---------+-------------+-----------+

I marked the x, xy and xyz I used to eliminate a 4, a 1 and a 6, all in that order. In the diagram, the rectangular x-wing should be obvious, the xy-wing is also comprised of the 12 and 18, and the zyz wing is also comprized of the 16 and 36.
Smile
Don D.
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania

PostPosted: Wed Oct 03, 2007 6:04 pm    Post subject: Daily Sudoku Oct 3-2007 Reply with quote

An XY-Wing with a pivot at r4c8{2,8} eliminating 1 at r6c4.After that the puzzle is solved by normal elimination.
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sheryl



Joined: 24 Sep 2007
Posts: 64
Location: New York

PostPosted: Wed Oct 03, 2007 6:07 pm    Post subject: 10/3 puzzle Reply with quote

duffy,
i appreciate the help. is there a particular book that you would suggest? i've read several different books, including an explanation in sudopedia, but i need the basics explained, e.g. what is an x wing or a y wing .. when the terms are used without the basic explanation it is just not understandable to me. i will study your diagram some more, but so far, it is not becoming clear to me. when you learned this, did you actually learn it from a book or did someone explain it to you? i think if someone actually showed me rather than tried to tell me i would be able to pick it up. i'm going to have a friend of mine sign up and read you explanations, maybe he can explain it to me.

anyway, i very much appreciate your trying and i will keep looking at your diagram, something might gel!
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Wed Oct 03, 2007 6:22 pm    Post subject: Reply with quote

Sheryl, if Sudopedia isn't helpful, try searching for the specific technique you're interested in. For example, search for "sudoku x-wing" (without the quote marks) and you'll have plenty of choices, increasing the odds that you'll find the type of explanation that suits you.
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duffy



Joined: 13 Sep 2007
Posts: 26
Location: Toronto Canada

PostPosted: Wed Oct 03, 2007 6:32 pm    Post subject: Reply with quote

Sheryl,
I haven't used any books, just lots of practice and follow-up on web entries. I have found, on this site, lots of good explanations by Marty and Keith, in particular. Also, Marty's search suggestion is a good one; a particular site with good explanations that I used recently is brainbashers.com. And remember, once again, that one normally won't be able to absorb too many complex descriptions at a time.
Idea
Don.
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sheryl



Joined: 24 Sep 2007
Posts: 64
Location: New York

PostPosted: Wed Oct 03, 2007 6:35 pm    Post subject: 10/3 puzzle Reply with quote

thanks everyone. i'll let you know how i do!
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Wed Oct 03, 2007 7:23 pm    Post subject: Reply with quote

As a matter of interest the BUG+3 pattern also eliminates 4 from r8c4.

Suppose you write the George and Peter’s grid in this form

Code:
+---------+-------------+---------+
| 4 5  2  | 13+6  8  16 | 7  36 9 |
| 8 6  7  | 9     23 24 | 34 1  5 |
| 9 3  1  | 46    7  5  | 8  46 2 |
+---------+-------------+---------+
| 3 18 9  | 7     4  12 | 5  28 6 |
| 7 18 6  | 5     12 3  | 9  28 4 |
| 2 4  5  | 8     6  9  | 1  7  3 |
+---------+-------------+---------+
| 5 7  34 | 2     9  8  | 6  34 1 |
| 6 9  34 | 14+3  13 7  | 2  5  8 |
| 1 2  8  | 36+4  5  46 | 34 9  7 |
+---------+-------------+---------+

The underling BUG pattern is evident – if all the candidates following the plus signs are omitted, each remaining candidate occurs precisely twice in each house.

To avoid the BUG at least one if the following has to be true:
- r1c4 contains 6
- r8c4 contains 3
- r9c4 contains 4.
The (46) in r3c4 means that 4 may be eliminated from r8c4 whichever case applies.

Steve
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Wed Oct 03, 2007 7:28 pm    Post subject: Reply with quote

Quote:
An XY-Wing with a pivot at r4c8{2,8} eliminating 1 at r6c4.After that the puzzle is solved by normal elimination.


Must have missed something. After the above xy wing I still needed a skyscraper on 3s in R29 to take out the 3 in R8C5.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Thu Oct 04, 2007 1:55 am    Post subject: Reply with quote

Given the techniques that the "very hard" puzzles may require, this one can be solved with an X-wing, and XY-wing, and an XYZ-wing.

After the first two, I get to here:
Code:
+-------------+-------------+-------------+
| 4   5   2   | 136 8   16  | 7   36  9   |
| 8   6   7   | 9   23  24  | 34  1   5   |
| 9   3   1   | 46  7   5   | 8   46  2   |
+-------------+-------------+-------------+
| 3   18  9   | 7   4   12  | 5   28  6   |
| 7   18  6   | 5   12  3   | 9   28  4   |
| 2   4   5   | 8   6   9   | 1   7   3   |
+-------------+-------------+-------------+
| 5   7   34  | 2   9   8   | 6   34  1   |
| 6   9   34  | 134 13  7   | 2   5   8   |
| 1   2   8   | 36  5   46  | 34  9   7   |
+-------------+-------------+-------------+

I happened to spot the BUG+2: Either R1C4 is <6> or R8C4 is <3>. They form a pair with R9C4 <36>, so R3C4 is <4>.

The XYZ-wing is <16> <136> <36> in R1C4, which also eliminates <6> in R3C4.

Keith
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