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Johan
Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium
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 Posted: Thu Jul 19, 2007 11:37 pm Post subject: 20 JULY VH |
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| I suppose this one was not so VH, one xy-chain solves the puzzle i think. |
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Captain Pete
Joined: 09 Jun 2007
Posts: 55
Location: Oley, PA
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| Posted: Fri Jul 20, 2007 1:51 pm Post subject: |
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| Could you describe the XY-Chain in this puzzle? |
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sdq_pete
Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL
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| Posted: Fri Jul 20, 2007 2:30 pm Post subject: |
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I found myself unable to get past the following point:
| Code: |
+------------+----------+----------+
| 8 36 369 | 5 1 29 | 23 4 7 |
| 17 167 469 | 3 69 249 | 28 68 5 |
| 2 5 346 | 8 67 47 | 1 36 9 |
+------------+----------+----------+
| 4 9 2 | 1 5 8 | 37 37 6 |
| 37 37 8 | 9 2 6 | 4 5 1 |
| 15 16 56 | 7 4 3 | 9 2 8 |
+------------+----------+----------+
| 9 4 7 | 2 8 5 | 6 1 3 |
| 35 2 35 | 6 79 1 | 78 789 4 |
| 6 8 1 | 4 3 79 | 5 79 2 |
+------------+----------+----------+
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Play this puzzle online at the Daily Sudoku site
Peter |
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Johan
Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium
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| Posted: Fri Jul 20, 2007 3:33 pm Post subject: XY-CHAIN |
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XY-chain length 4.
Starting with number 2 in [R1C6] = 3 in [R1C7] = 6 in [R3C8] = 7 in [R3C5(chain end)].
Starting with number 9 in [R1C6] = 7 in [R9C6].
This means either 7 resides in [R3C5] or in [R9C6] or in both [R3C5,R9C6]
Both cells [R3C5,R9C6] can see the bi-value cell [47] in R3C6, which eliminates the 7 from R3C6, that solves the puzzle.
Both 7's in R2C5 and R2C6 must be erased in the grid, I couldn't delete them before copying and pasting.
[/code]
| Code: |
+------------+-------------+----------+
| 8 136 369 | 5 169 29 | 23 4 7 |
| 17 167 469 | 3 1679 2479 | 28 68 5 |
| 2 5 346 | 8 67 47 | 1 36 9 |
+------------+-------------+----------+
| 4 9 2 | 1 5 8 | 37 37 6 |
| 37 37 8 | 9 2 6 | 4 5 1 |
| 15 16 56 | 7 4 3 | 9 2 8 |
+------------+-------------+----------+
| 9 4 7 | 2 8 5 | 6 1 3 |
| 35 2 35 | 6 79 1 | 78 789 4 |
| 6 8 1 | 4 3 79 | 5 79 2 |
+------------+-------------+----------+
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[/quote] |
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jLo
Joined: 30 Apr 2007
Posts: 55
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| Posted: Fri Jul 20, 2007 3:57 pm Post subject: |
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| sdq_pete wrote: | I found myself unable to get past the following point:
| Code: |
+------------+----------+----------+
| 8 36 369 | 5 1 29 | 23 4 7 |
| 17 167 469 | 3 69 249 | 28 68 5 |
| 2 5 346 | 8 67 47 | 1 36 9 |
+------------+----------+----------+
| 4 9 2 | 1 5 8 | 37 37 6 |
| 37 37 8 | 9 2 6 | 4 5 1 |
| 15 16 56 | 7 4 3 | 9 2 8 |
+------------+----------+----------+
| 9 4 7 | 2 8 5 | 6 1 3 |
| 35 2 35 | 6 79 1 | 78 789 4 |
| 6 8 1 | 4 3 79 | 5 79 2 |
+------------+----------+----------+
|
Play this puzzle online at the Daily Sudoku site
Peter |
Notice that the <6> in row 1 will be from box 1. That eliminates the <6> entries
in box 1 that are not in row 1 (R2C2, R2C3 and R3C3). This opens up an XYZ-wing
with a pivot in box 2. |
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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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| Posted: Fri Jul 20, 2007 6:20 pm Post subject: July 20 VH |
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Peter,
On your grid there is a four-step xy chain beginning at R9C6, ending at R4C8 which removes the 7 from R9C8, and opens the puzzle.
Earl |
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sdq_pete
Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL
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| Posted: Fri Jul 20, 2007 6:52 pm Post subject: |
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| jLo wrote: |
Notice that the <6> in row 1 will be from box 1. That eliminates the <6> entries
in box 1 that are not in row 1 (R2C2, R2C3 and R3C3). |
I can't believe I missed that!
| Earl wrote: | | there is a four-step xy chain beginning at R9C6, ending at R4C8 which removes the 7 from R9C8 |
I'm not sure I understand this. I presume you are referring to the strong link chain of 7's but I can't follow it to R4C8 (there are 3 candidate 7's on row 8 ).
Incidentally, this is probably more trial and error, but in box 3, setting either R3C8 to 3 or R2C8 to 6 quickly leads in both cases to duplicate values (illogical state) showing that the values must be 6 and 8 respectively. Perhaps not the most satsfactory solution though.
Peter |
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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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| Posted: Fri Jul 20, 2007 9:11 pm Post subject: July 20 VH |
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Peter,
It is an xy chain, not a strong link of 7's.
If R9C6 is 7, R9C8 cannot be 7.
If R9C6 is 9, R9C8 cannot be 7 because R4C8 is 7.
(If R9C6 is 9, R8C5 is 7, R3C5 is 6, R3C8 is 3, and R4C8 is 7).
Earl |
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sdq_pete
Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL
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| Posted: Sat Jul 21, 2007 11:53 am Post subject: |
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Hi Earl
Ah, is that an XY chain? It actually seems a similar argument to what I mentioned myself - a presumed value leading to a logical impasse. Is there anything special about that route? I mean, I could just as easily have said, if R9C6 = 9, then R1C6 = 2, R1C7 = 3 and R4C7 = 7... So, is there something special about your route to R4C8 = 7 or is it trial and error?
Peter |
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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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| Posted: Sat Jul 21, 2007 6:21 pm Post subject: July 20 VH |
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Peter,
I suppose any chain can be thought of as trial and error, but an xy chain does have a pincer effect which is logic. One might think of an xy chain as an xy wing with one arm extended.
Earl |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Sat Jul 21, 2007 7:33 pm Post subject: |
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I know I'm coming in late on this discussion, but the puzzle can be solved with a couple of XYZ-wings.
Keith |
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