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kragzy
Joined: 01 May 2007
Posts: 112
Location: Australia
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 Posted: Mon May 21, 2007 11:05 pm Post subject: VH 21 May |
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Just when I thought I was getting reasonably competent... I can't seem to find a way past this point. The puzzle looks like it there is a lot more "cleaning up" to do and I fear that I have missed something really obvious. Please help (and be gentle!).
| Code: |
+-------------+-----------------+------------+
| 1 4 9 | 256 3 256 | 8 256 7 |
| 256 8 3 | 2569 249 7 | 1 2456 29 |
| 7 25 26 | 1 8 24569 | 69 456 3 |
+-------------+-----------------+------------+
| 8 1 7 | 4 6 3 | 2 9 5 |
| 249 6 24 | 58 29 58 | 3 7 1 |
| 29 3 5 | 29 7 1 | 4 8 6 |
+-------------+-----------------+------------+
| 26 279 1 | 26789 5 2689 | 69 3 4 |
| 456 59 8 | 3 1 469 | 7 26 29 |
| 3 279 246 | 2679 249 2469 | 5 1 8 |
+-------------+-----------------+------------+
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Many thanks. |
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George Woods
Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK
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| Posted: Mon May 21, 2007 11:11 pm Post subject: |
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This is almost certainly a maverick solution but here we go
| Code: |
+---------+-------+-------+
| 1 4 9 | . 3 . | 8 . 7 |
| 256 8 3 | . . 7 | 1 . . |
| 7 . . | 1 8 . | . . 3 |
+---------+-------+-------+
| 8 1 7 | 4 6 3 | 2 9 5 |
| 249 6 . | . . . | 3 7 1 |
| 29 3 5 | . 7 1 | 4 8 6 |
+---------+-------+-------+
| 269 . 1 | . 5 . | . 3 4 |
| . . 8 | 3 1 . | 7 . . |
| 3 . . | . . . | 5 1 8 |
+---------+-------+-------+
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Play this puzzle online at the Daily Sudoku site
Once again I differ from the "official route"
Looking at the 249, 29, and 269 (yes this should be 26!) in col 1, I noted that an "external" 6 would release the 4 in box4 and an "external" 4 the 6 in box 7 BUT the 6 in Box1 would release the 4 in box2 creating a pair of 46s bearing down impossibly on box 7 hence r2c1 cannot be 6.
More formally-
If r2c1 is 6 then r5c1 is 4 and "overstrained" r9c3 has to be both 4 and 6
so r2c1 cannot be 6 r3c3=6..... and on to an easy solution |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Mon May 21, 2007 11:20 pm Post subject: |
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Hint: Look for an XY-wing.
| Code: | +-------------------+-------------------+-------------------+
| 1 4 9 | 256 3 256 | 8 256 7 |
| 256 8 3 | 2569 249 7 | 1 2456 29 |
| 7 25 26 | 1 8 24569 | 69 456 3 |
+-------------------+-------------------+-------------------+
| 8 1 7 | 4 6 3 | 2 9 5 |
| 249 6 24 | 58 29 58 | 3 7 1 |
| 29 3 5 | 29 7 1 | 4 8 6 |
+-------------------+-------------------+-------------------+
| 26 279 1 | 26789 5 2689 | 69 3 4 |
| 456 59 8 | 3 1 469 | 7 26 29 |
| 3 279 246 | 2679 249 2469 | 5 1 8 |
+-------------------+-------------------+-------------------+ |
n
n
n
n
n
n
n
n
n
Strong Hint: Look at one of the <69> cells.
Keith
Last edited by keith on Mon May 21, 2007 11:31 pm; edited 1 time in total |
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kragzy
Joined: 01 May 2007
Posts: 112
Location: Australia
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| Posted: Mon May 21, 2007 11:26 pm Post subject: |
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Well I can see what you're saying, but I have no idea how I would go about finding such things!
Many thanks for your post George (and you're up very late in Dorset!). Is there a "method" to find this type of elimination, or do you just have a bizarre streak of logic?
Cheers |
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kragzy
Joined: 01 May 2007
Posts: 112
Location: Australia
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| Posted: Mon May 21, 2007 11:38 pm Post subject: |
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Keith, thanks. Found it and solved it. I knew it would be something that I should have seen.
Cheers |
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michelle.mcclure@gmail.co
Joined: 22 May 2007
Posts: 1
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| Posted: Tue May 22, 2007 12:33 am Post subject: |
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Alas, I found at least two X-Y wings (or at least part of them), but didn't manage to get any farther than this:
+-------------------+-------------------+-------------------+
| 1 4 9 | 256 3 256 | 8 256 7 |
| 56 8 3 | 2569 249 7 | 1 2456 29 |
| 7 25 26 | 1 8 24569 | 69 456 3 |
+-------------------+-------------------+-------------------+
| 8 1 7 | 4 6 3 | 2 9 5 |
| 249 6 24 | 58 29 58 | 3 7 1 |
| 29 3 5 | 29 7 1 | 4 8 6 |
+-------------------+-------------------+-------------------+
| 26 79 1 | 26789 5 2689 | 69 3 4 |
| 456 59 8 | 3 1 469 | 7 26 29 |
| 3 279 246 | 2679 249 2469 | 5 1 8 |
+-------------------+-------------------+-------------------+
So, I"m missing the correct x-y wing, or I'm not seeing the obvious next step. Any additional hints most welcome!
Thanks, |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Tue May 22, 2007 1:38 am Post subject: |
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| Quote: | | So, I"m missing the correct x-y wing, or I'm not seeing the obvious next step. Any additional hints most welcome! |
| Code: | +-------------------+-------------------+-------------------+
| 1 4 9 | 256 3 256 | 8 256 7 |
| 56 8 3 | 2569 249 7 | 1 2456 29 |
| 7 25 26 | 1 8 24569 | 69 456 3 |
+-------------------+-------------------+-------------------+
| 8 1 7 | 4 6 3 | 2 9 5 |
| 249 6 24 | 58 29 58 | 3 7 1 |
| 29 3 5 | 29 7 1 | 4 8 6 |
+-------------------+-------------------+-------------------+
| 26 79 1 | 26789 5 2689 | 69 3 4 |
| 456 59 8 | 3 1 469 | 7 26 29 |
| 3 279 246 | 2679 249 2469 | 5 1 8 |
+-------------------+-------------------+-------------------+ |
Take a look at the XY-Wing based in r2c1. |
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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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| Posted: Tue May 22, 2007 11:49 am Post subject: |
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| George's logic seems to be an "if this is this - then that is that" solution. That's like guessing. |
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Nwohio
Joined: 12 May 2007
Posts: 9
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| Posted: Tue May 22, 2007 7:45 pm Post subject: |
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| cgordon wrote: | | George's logic seems to be an "if this is this - then that is that" solution. That's like guessing. |
While I see where you are coming from, isn't "if this, this and if that, that" what so many of the conventional solving techniques rely on? |
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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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| Posted: Tue May 22, 2007 8:35 pm Post subject: |
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| I personally don't think so. Until recently, I'd get as far as I could with the "very hard" puzzles and then make a guess. Theoretically I could do this iteration right off the bat. Now I look for these XYZ or XY wing things or "skyscraper" patterns. Looking for these usually takes me longer than the guessing. But I feel I can now reach the solution without making an assumption. Perhaps it's a philosophical argument. |
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Leon J. Taub
Joined: 22 May 2007
Posts: 2
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| Posted: Tue May 22, 2007 10:58 pm Post subject: VH21May |
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Wouldn't the following analysis be a variant of a "unique rectangle" ?:
Note the "29s" in R6C1, R6C4 & R5C5. The 29 in R5C1 may therefore be removed, leaving only the 4. The puzzle solves easily from this point. |
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George Woods
Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK
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| Posted: Tue May 22, 2007 11:28 pm Post subject: Re: VH21May |
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| Leon J. Taub wrote: | Wouldn't the following analysis be a variant of a "unique rectangle" ?:
Note the "29s" in R6C1, R6C4 & R5C5. The 29 in R5C1 may therefore be removed, leaving only the 4. The puzzle solves easily from this point. |
An UR has to be a rectangle and your one is not one. so the conclusion you reach may well be right but this is just chance! |
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George Woods
Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK
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| Posted: Tue May 22, 2007 11:31 pm Post subject: |
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| cgordon wrote: | | I personally don't think so. Until recently, I'd get as far as I could with the "very hard" puzzles and then make a guess. Theoretically I could do this iteration right off the bat. Now I look for these XYZ or XY wing things or "skyscraper" patterns. Looking for these usually takes me longer than the guessing. But I feel I can now reach the solution without making an assumption. Perhaps it's a philosophical argument. |
My attitude is - If I can see it without recourse to using a pencil then it is not trial and error.
As a matter of fact I saw this before recognizing the effect of the 9s in box7 (without which I couldn't see the XY wing!) |
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Leon J. Taub
Joined: 22 May 2007
Posts: 2
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| Posted: Wed May 23, 2007 1:56 am Post subject: VH21May |
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| Thanks for your comment, George. I see now that the UR MUST be a rectangle! |
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peter.s
Joined: 29 May 2007
Posts: 2
Location: Belgium
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| Posted: Tue May 29, 2007 7:49 pm Post subject: |
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sorry Marty R. but I don't see it :
Take a look at the XY-Wing based in r2c1
please help ! |
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David
Joined: 02 Jun 2006
Posts: 58
Location: Bedford, UK
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| Posted: Tue May 29, 2007 8:09 pm Post subject: |
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Peter S
If you look at r2c1 (56), r3c2 (25) and r7c1 (26) they form an XY wing and the two pincers can be used to eliminate the '2' in r9c2. This leaves you with a naked pair (79) in c2 which should help you considerably. |
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peter.s
Joined: 29 May 2007
Posts: 2
Location: Belgium
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| Posted: Tue May 29, 2007 8:25 pm Post subject: |
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David
Thanks , I did not see that the 2 of r9c2 was involved in the XY-wing ! |
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