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msgraciey
Joined: 02 May 2007
Posts: 6
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 Posted: Thu May 10, 2007 2:40 am Post subject: April 27 |
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Help?
612 387 945
345 269 781
897 1 45 45 236
1259 26 8 4 159 3 56 7 29
2459 3 49 69 7 56 58 1 289
15 7 69 8 15 2 4 69 3
753 69 49 1 68 2 48
249 28 469 5 3 48 1 69 7
49 68 1 7 2 68 3 5 49
I tried several susser type programs but I don't get it! Thanks! |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Thu May 10, 2007 5:01 am Post subject: |
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| Code: | -------------------------------------------------
|6 1 2 |3 8 7 |9 4 5 |
|3 4 5 |2 6 9 |7 8 1 |
|8 9 7 |1 45 45 |2 3 6 |
-------------------------------------------------
|1259 26 8 |4 159 3 |56 7 29 |
|2459 3 49 |69 7 56 |58 1 289 |
|15 7 69 |8 15 2 |4 69 3 |
-------------------------------------------------
|7 5 3 |69 49 1 |68 2 48 |
|249 28 469 |5 3 48 |1 69 7 |
|49 68 1 |7 2 68 |3 5 49 |
------------------------------------------------- |
There is an XY-Wing 29-69-26 based in r4c9. That takes out the 6 in r6c3. If it doesn't solve the puzzle, it will at least make a dent. |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Thu May 10, 2007 10:11 am Post subject: |
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The UR on <15> solves it.
Keith |
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msgraciey
Joined: 02 May 2007
Posts: 6
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| Posted: Thu May 10, 2007 11:56 am Post subject: |
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| I was given that as a tip. What I don't understand is that there are other 2s, 6s and 9s within those cells. How then does the xywing work? Thanks for your educational help! |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Thu May 10, 2007 4:51 pm Post subject: |
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The basic XY-Wing rule is: start with any bivalue cell, which we call XY. That cell must see two other cells, which we call XZ and YZ. Then any cell which sees both XZ and YZ cannot contain Z.
In the actual example, our XY cell is the 29 and XZ and YZ are the 26 and 69. If you test the 29 cell for either value, you will see that one of the other two must contain a 6, thus r6c3 can't be a 6 because it sees both the XZ and YZ cells, one of which must be a 6.
Keith mentioned the UR (Unique Rectangle) solves the puzzle. If you are not familiar with URs, see his primer on them at:
http://www.sudoku.com/forums/viewtopic.php?p=29105#29105 |
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msgraciey
Joined: 02 May 2007
Posts: 6
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| Posted: Fri May 11, 2007 5:56 pm Post subject: |
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| Here's where I'm still not getting it. In the row with the xy, if you choose the 2, then I can sort of see other things getting eliminated. But if you choose the 9, I'm not clear on how that would eliminate things, as there are other 9s, 6s and 2s in the various cells in question. How do you know?! Thanks! |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Fri May 11, 2007 9:21 pm Post subject: |
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| msgraciey wrote: | | Here's where I'm still not getting it. In the row with the xy, if you choose the 2, then I can sort of see other things getting eliminated. But if you choose the 9, I'm not clear on how that would eliminate things, as there are other 9s, 6s and 2s in the various cells in question. How do you know?! Thanks! |
OK, let's see if we can clear this up. Try and concentrate on the XY-XZ-YZ cells and block out the other clutter. Our XY cell is r4c9. If that cell is 2, then r4c2 (XZ) must be 6. If r4c9 is 9, then r6c8 (YZ) must be 6. It's that simple, one or the other must be a 6. Since r6c3 sees both cells of which one has to be a 6, then r6c3 can't be a 6. Hope that helps. The XY-Wing is often used in the VH puzzles here, so familiarity with that technique is key to solving many of them.
| Code: | -------------------------------------------------
|6 1 2 |3 8 7 |9 4 5 |
|3 4 5 |2 6 9 |7 8 1 |
|8 9 7 |1 45 45 |2 3 6 |
-------------------------------------------------
|1259 26 8 |4 159 3 |56 7 29 |
|2459 3 49 |69 7 56 |58 1 289 |
|15 7 69 |8 15 2 |4 69 3 |
-------------------------------------------------
|7 5 3 |69 49 1 |68 2 48 |
|249 28 469 |5 3 48 |1 69 7 |
|49 68 1 |7 2 68 |3 5 49 |
------------------------------------------------- |
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