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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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 Posted: Sat Oct 20, 2007 12:37 pm Post subject: Oct 20 DB |
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Here is the Oct 20 DB as in the St. Louis paper.
I did it with two xy-chains. Hope someone finds a neater solution.
Earl
| Code: |
+-------+-------+-------+
| . 2 . | 5 1 . | . . . |
| . 8 . | . 6 . | 1 . 2 |
| . . . | . . 8 | 3 6 . |
+-------+-------+-------+
| 2 . . | 3 . . | . 8 1 |
| . 9 5 | . . . | 6 2 . |
| 1 7 . | . . 6 | . . 4 |
+-------+-------+-------+
| . 3 2 | 9 . . | . . . |
| 4 . 9 | . 7 . | . 3 . |
| . . . | . 3 2 | . 7 . |
+-------+-------+-------+
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Play this puzzle online at the Daily Sudoku site |
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TKiel
Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI
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| Posted: Sat Oct 20, 2007 1:14 pm Post subject: |
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Basics stop here:
| Code: |
*--------------------------------------------------*
| 369 2 67 | 5 1 379 | 89 4 78 |
| 359 8 47 | 47 6 39 | 1 59 2 |
| 59 45 1 | 247 29 8 | 3 6 57 |
|----------------+----------------+----------------|
| 2 46 46 | 3 59 59 | 7 8 1 |
| 8 9 5 | 17 4 17 | 6 2 3 |
| 1 7 3 | 28 28 6 | 59 59 4 |
|----------------+----------------+----------------|
| 7 3 2 | 9 58 4 | 58 1 6 |
| 4 16 9 | 168 7 15 | 2 3 58 |
| 56 156 8 | 16 3 2 | 4 7 9 |
*--------------------------------------------------*
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Seemingly worthless <156> XY-wing with pivot at r8c2. Coloring the pincers leads to the exclusion of <5> in r3c1 and solves the puzzle. |
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Johan
Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium
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| Posted: Sat Oct 20, 2007 3:20 pm Post subject: |
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| A 7-cell XY-chain starting with <6> in R9C1, that ends with <5> in R3C1, which erases <5> in R2C1, was the final step for me. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sat Oct 20, 2007 3:24 pm Post subject: |
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| I eliminated the 9 from r1c1 to break up the deadly pattern, but that move affected nothing. But I then spotted the XY-Wing and made the identical move as Tracy did to finish it off. I just want to add that the coloring of pincers is a new technique to me within the last month or so and it has turned out to be a very powerful weapon. |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Sun Oct 21, 2007 6:00 pm Post subject: |
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| Code: | +-------------+-------------+-------------+
| 369 2 67 | 5 1 379 | 89 4 78 |
| 35-9 8 47 | 47 6 39 | 1 59$ 2 |
| 59$ 45 1 | 247 29 8 | 3 6 57 |
+-------------+-------------+-------------+
| 2 46 46 | 3 59# 59 | 7 8 1 |
| 8 9 5 | 17 4 17 | 6 2 3 |
| 1 7 3 | 28 28 6 | 59# 59 4 |
+-------------+-------------+-------------+
| 7 3 2 | 9 58@ 4 | 58@ 1 6 |
| 4 16 9 | 168 7 15 | 2 3 58 |
| 56 156 8 | 16 3 2 | 4 7 9 |
+-------------+-------------+-------------+ |
Marty has pointed out the Unique X-wing on <39> in R12C16. You can eliminate <9> from R1C1.
There is also a UR on <16> in R89C24. With strong links on <1> and <6>, you can take out <1> from R8C4 and <6> from R9C2.
None of these eliminations are of any help.
There is a W-wing on <9>: With the strong link on <5> marked @, one or both of the cells marked # is <9>. Then, by coloring, one or both of the cells marked $ is <9>, and you can eliminate <9> as a candidate in R2C1.
The result is the same as that obtained by Tracy.
Keith |
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dejsmith
Joined: 23 Oct 2005
Posts: 42
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| Posted: Tue Oct 23, 2007 7:11 pm Post subject: |
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Marty, Tracy
As usual, I am a few days behind; but I seem to have been gone for the discussion on "coloring the pincers". Could you explain that or point me in the right direction to read about this technique? I gave up & settled on solving this puzzle with a contradiction off of the R89C24 UR.
Thanks...Dave |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Tue Oct 23, 2007 9:32 pm Post subject: |
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Dave,
Let me try with an example.
| Code: |
+--------+--------+---------+
| . . . | . . . | . . . |
| . . . | . . . | . . . |
| . . . | . . . | . 345 . |
+--------+--------+---------+
| . . . | . . . | . . . |
| . . . | . . . | . . . |
| 34 . . | . . . | . . . |
+--------+--------+---------+
| . . . | . . . | . . . |
| . . . | . . . | . . . |
| 24 . . | 23 . . | . 368 . |
+--------+--------+---------+
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Play this puzzle online at the Daily Sudoku site
Note the XY-Wing in the lower left, which has 3 as the pincer number. Assume the two trivalue cells are strong links on 3. So we create a three-cell chain on 3. If the pincer in r9c4 is a 3, then r3c8 must also be a 3 because of the strong links, so r3c8 also works as a pincer with r6c1 and creates further potential eliminations.
Hope that's clear enough. |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Tue Oct 23, 2007 10:41 pm Post subject: |
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Dave,
Take a look at this:
http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=2028
The result of a W-wing is the same as that of an XY-wing: One, or both of two pincer cells must be W (or Z). With coloring, you can extend the pincer cells to other cells that must have the same value.
I agree with Marty that this is a very powerful technique. We should probably rewrite the explanation given in the link above, now that our understanding has matured.
Best wishes,
Keith |
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dejsmith
Joined: 23 Oct 2005
Posts: 42
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| Posted: Wed Oct 24, 2007 4:56 pm Post subject: |
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Thanks guys
As usual, I have printed out the link because I am sure this will take me a while to absorb. Thanks for continuing your efforts to enlighten us all on Sam's site. Although I do not write often since I am always behind in my puzzle solving, I continue to read & enjoy learning from all of you.
Dave |
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