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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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 Posted: Sat Apr 25, 2009 2:39 am Post subject: April 25 VH |
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This one takes more than the customary xy-wing.
SOLUTIONS: Coloring <6> eliminates <6> from R9C4; or an xy-chain eliminates <9> from R2C1, each a single-step solution.
Early Earl
PS See a correction below. The old reliable xy-wing does it again.
Last edited by Earl on Sat Apr 25, 2009 1:44 pm; edited 2 times in total |
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crunched
Joined: 05 Feb 2008
Posts: 168
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| Posted: Sat Apr 25, 2009 3:19 am Post subject: Re: April 25 VH |
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| Earl wrote: | This one takes more than the customary xy-wing.
SOLUTIONS: Coloring <6> eliminates <6> from R9C4; or an xy-chain eliminates <9> from R2C1, each a single-step solution.
Early Earl |
NOPE, an xy wing is all ya need. See the grid below for the xy wing (hint: the pivot is in box 3)---which solves the puzzle. But...I don't think that any wing of any kind is needed here. The grid below clearly has more basic clutter that can be removed. I started to post this grid, and decided to go ahead and take out the rest of the basics that I could see. Guess what? I kept going and I solved the puzzle without the xy (or any other wing).
| Code: |
+-------------+---------------+----------------+
| 4 679 8 | 3 5 169 | 67 2 17 |
| 79 679 1 | 469 2 469 | 34567 8 3457 |
| 3 2 5 | 146 8 7 | 9 46 14 |
+-------------+---------------+----------------+
| 6 4 27 | 789 1 389 | 238 5 39 |
| 1 8 9 | 2 34 5 | 34 7 6 |
| 5 3 27 | 4789 6 489 | 248 1 49 |
+-------------+---------------+----------------+
| 8 17 6 | 5 9 14 | 47 3 2 |
| 2 579 347 | 4678 347 3468 | 1 469 4579 |
| 79 1579 347 | 1467 347 2 | 4567 469 8 |
+-------------+---------------+----------------+
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Play this puzzle online at the Daily Sudoku site |
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gindaani
Joined: 06 Mar 2009
Posts: 79
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| Posted: Sun Apr 26, 2009 1:35 am Post subject: |
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I had this after the basics:
| Code: |
+------------+---------------+--------------+
| 4 69 8 | 3 5 169 | 67 2 17 |
| 79 679 1 | 469 2 469 | 35 8 35 |
| 3 2 5 | 16 8 7 | 9 46 14 |
+------------+---------------+--------------+
| 6 4 27 | 789 1 389 | 28 5 39 |
| 1 8 9 | 2 34 5 | 34 7 6 |
| 5 3 27 | 4789 6 489 | 28 1 49 |
+------------+---------------+--------------+
| 8 17 6 | 5 9 14 | 47 3 2 |
| 2 579 34 | 468 347 3468 | 1 469 457 |
| 79 1579 34 | 146 347 2 | 4567 469 8 |
+------------+---------------+--------------+
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Play this puzzle online at the Daily Sudoku site
I couldn't find any more basics, but the old xy-wing is a one stepper.
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Louise56
Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA
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| Posted: Sun Apr 26, 2009 10:00 pm Post subject: |
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| I can't see the xy wing. I solved the puzzle with what I thought was a skyscraper using the 4s in rows 5 & 7. I looked at them and eliminated the 4 in r6c6 and then eliminated the 4s in box 8 c5. I would appreciate more info on the xy wing. Thanks. |
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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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| Posted: Sun Apr 26, 2009 11:50 pm Post subject: |
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Louise,
The pivot of the xy-wing is R1C7; the "wings" are R3C8 and R9C7 which eliminate any <4> that "sees" both of these wings.
Earl |
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Louise56
Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA
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| Posted: Mon Apr 27, 2009 12:28 am Post subject: |
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Thanks Earl. I do have a hard time finding the wings. Hopefully this will improve with practice.  |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Mon Apr 27, 2009 1:57 am Post subject: |
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| Quote: | | Hopefully this will improve with practice |
Louise56,
over in the "puzzles by Daj" section of the forum are many VH type puzzles with which you can practice. |
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crunched
Joined: 05 Feb 2008
Posts: 168
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| Posted: Mon Apr 27, 2009 2:07 am Post subject: |
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WOW, you can find skyscrapers but not wings?
I can NEVER spot those 'scrapers.
| Louise56 wrote: | | Thanks Earl. I do have a hard time finding the wings. Hopefully this will improve with practice. |
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Louise56
Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA
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| Posted: Mon Apr 27, 2009 3:04 am Post subject: |
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Thanks guys for the help. I love to kickstart my brain with these puzzles!  |
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Ema Nymton
Joined: 17 Apr 2009
Posts: 89
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| Posted: Mon Apr 27, 2009 12:02 pm Post subject: |
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.
This is one challenging puzzle!
I find myself at the identical point in this puzzle.
Please 'bare' with me ;) I do not 'see' the reason nor logic at choosing any of the choices at this point of the puzzle.
But is not using wings just another form of guessing? At this point in the puzzle, choosing a 4 at _r3c8_ is a 50/50 odds, so why pick?
. |
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Ema Nymton
Joined: 17 Apr 2009
Posts: 89
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| Posted: Mon Apr 27, 2009 1:20 pm Post subject: Re: April 25 VH |
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I am with you up to this point.
What is your next logical selection, and _why_? Each possible choice seems as logical as any other. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Mon Apr 27, 2009 3:37 pm Post subject: |
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| Quote: | | But is not using wings just another form of guessing? At this point in the puzzle, choosing a 4 at _r3c8_ is a 50/50 odds, so why pick? |
Ema,
Using wings is not guessing, because they involve a proven pattern with the same general effect. We don't "choose" a 4 in r3c8, the 4 falls into place as a result of eliminations resulting from the 67-47-46 XY-Wing. |
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Louise56
Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA
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| Posted: Mon Apr 27, 2009 4:39 pm Post subject: |
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Ema,
It is true that with guessing you can often solve the puzzles faster, but the art of solving sudoku is to have a logical reason for each step. It's like a geometry proof in that you have to say why you are eliminating a number or putting one in. Below is the puzzle as crunched posted.
| Code: | +------------+---------------+--------------+
| 4 69 8 | 3 5 169 | 67 2 17 |
| 79 679 1 | 469 2 469 | 35 8 35 |
| 3 2 5 | 16 8 7 | 9 46 14 |
+------------+---------------+--------------+
| 6 4 27 | 789 1 389 | 28 5 39 |
| 1 8 9 | 2 34 5 | 34 7 6 |
| 5 3 27 | 4789 6 489 | 28 1 49 |
+------------+---------------+--------------+
| 8 17 6 | 5 9 14 | 47 3 2 |
| 2 579 34 | 468 347 3468 | 1 469 457 |
| 79 1579 34 | 146 347 2 | 4567 469 8 |
+------------+---------------+--------------+
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If you look in box 3 you can see the 67 pair and the 46 pair. When looking for an xy wing (which I am not very good at) you want to find a third pair to go with these two. Since they both have 6s in them you want to find a 47 pair to go with them. Then you have 3 pairs with three numbers. To be a wing one of the pairs must "see" the other two pairs. That means it must be either in the same box or along the same row or column. The three pairs can't be in the same box. So now that we have found the 67 and 46 pairs we look in the puzzle for a 47 pair and find it in box 9. It will work because the 67 pair can see the 46 pair and the 47 pair. Now look at the 67 pair. It will be either a 6 or a 7. If it is a 6 then the 46 pair will be a 4 and all the 4s below it in the column in can be eliminated. That takes out the 4s in column 8 in box 9. If the 67 pair is a 7 then th 47 pair will be a 4 which will also eliminate the 4s in column 8 in box 9. So you can conclude with logic that the 4s in c8, box 9 must be eliminated. |
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Ema Nymton
Joined: 17 Apr 2009
Posts: 89
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| Posted: Mon Apr 27, 2009 4:53 pm Post subject: |
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| Louise56 wrote: | Ema,
It is true that with guessing you can often solve the puzzles faster, but the art of solving sudoku is to have a logical reason for each step. It's like a geometry proof in that you have to say why you are eliminating a number or putting one in. Below is the puzzle as crunched posted.. |
Thank you. Your explanation is clear. Now let me see if it works for me.
Thanx again
~@:o?
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Tue Apr 28, 2009 12:54 am Post subject: |
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The XY-Wing can be defined as follows:
Start with a bivalue cell we'll call XY (the 67). This cell must see an XZ cell (the 46). XY must also see a YZ cell (the 47). Any cell(s) seeing both XZ and YZ may not contain -Z-. |
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Ema Nymton
Joined: 17 Apr 2009
Posts: 89
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| Posted: Tue Apr 28, 2009 9:10 am Post subject: |
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| Marty R. wrote: | The XY-Wing can be defined as follows:
Start with a bivalue cell we'll call XY (the 67). XY must also see a YZ cell (the 47). Any cell(s) seeing both XZ and YZ may not contain -Z-. |
Please forgive me for being such a stickler. At this point in this puzzle (early, half the puzzle is not 'solved'), the XY-Wing does get one over the hump, but one does have to be careful with terms.
Start with a bivalue cell we'll call XY (the 67). X = 6, Y = 7
This cell must see an XZ cell (the 46). ?X = 4, Z = 6?
XY must also see a YZ cell (the 47). ?Y = 4, Z = 7?
Any cell(s) seeing both XZ and YZ may not contain -Z-. ??
Your explanation makes sense in the global aspects of solving the puzzle, I just get lost in the specifics. In this puzzle , "Any cell(s) seeing both XZ and YZ may not contain -Z-." Which Z?
~@:o?
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Tue Apr 28, 2009 2:14 pm Post subject: |
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Ema,
If you do a Google search on: sudoku xy wing
you will find lots of help. Or, search for: sudopedia
Here is one explanantion of an xy-wing:
http://www.brainbashers.com/sudokuxywing.asp
Good luck!
Keith |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Tue Apr 28, 2009 4:36 pm Post subject: |
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| Quote: | Start with a bivalue cell we'll call XY (the 67). X = 6, Y = 7
This cell must see an XZ cell (the 46). ?X = 4, Z = 6?
XY must also see a YZ cell (the 47). ?Y = 4, Z = 7?
Any cell(s) seeing both XZ and YZ may not contain -Z-. ??
Your explanation makes sense in the global aspects of solving the puzzle, I just get lost in the specifics. In this puzzle , "Any cell(s) seeing both XZ and YZ may not contain -Z-." Which Z? |
Ema,
In your example above, you started out correctly defining XY as being = 67. Z can be any other number, in this case 4. So Z can't be 6 or 7, as you ask on lines 2 and 3 above, since they've already been defined as X and Y. |
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