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May 1, VH
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Tue May 01, 2007 3:29 pm    Post subject: May 1, VH Reply with quote

I solved it after two or three sessions. I was wondering whether others reached the same situation and found the same solution - what unlocked it for me was a sort of "skew" XY-wing. The situation was as follows:

Code:

+-------------+----------+-------------+
| 59  2   8   | 35 1  39 | 7   6   4   |
| 6   3   4   | 58 2  7  | 9   58  1   |
| 179 157 79  | 6  89 4  | 358 38  2   |
+-------------+----------+-------------+
| 3   6   279 | 1  5  89 | 28  4   78  |
| 8   4   5   | 7  3  2  | 1   9   6   |
| 179 17  279 | 4  89 6  | 238 378 5   |
+-------------+----------+-------------+
| 2   78  36  | 9  4  5  | 68  1   378 |
| 4   58  36  | 38 7  1  | 568 2   9   |
| 57  9   1   | 2  6  38 | 4   578 378 |
+-------------+----------+-------------+

Play this puzzle online at the Daily Sudoku site

What I noticed was the 79 at R3C3, the 89 in R3C5 and the 78 in R4C9 and wondered whether they formed a sort of indirect XY-wing via the 89's in block 5. Well, they did and this eliminated a 7 in R4C3.
Is this how others did it?

Peter
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Tue May 01, 2007 4:02 pm    Post subject: Reply with quote

I haven't done the puzzle yet, but what you did I know as "XY-Wing Chain", where if you have a chain of a pair with an odd number of cells, the start and end cells of the chain work as an XY-Wing.
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Golfgal



Joined: 31 Jul 2006
Posts: 7

PostPosted: Tue May 01, 2007 7:30 pm    Post subject: Reply with quote

How did you get the 6 in row 4, column 2?
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Mesmin



Joined: 01 May 2007
Posts: 12
Location: Ontario

PostPosted: Tue May 01, 2007 7:49 pm    Post subject: Reply with quote

Golfgal wrote:
How did you get the 6 in row 4, column 2?


3 steps to get the 6 in r4c2.

An X-wing, an XY-Wing, then a naked pair.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Wed May 02, 2007 12:41 am    Post subject: Reply with quote

Code:
+-------------+----------+-------------+
| 59  2   8   | 35 1  39 | 7   6   4   |
| 6   3   4   | 58 2  7  | 9   58  1   |
| 179 157 79  | 6  89 4  | 358 38  2   |
+-------------+----------+-------------+
| 3   6   279 | 1  5  89 | 28  4   78  |
| 8   4   5   | 7  3  2  | 1   9   6   |
| 179 17  279 | 4  89 6  | 238 378 5   |
+-------------+----------+-------------+
| 2   78  36  | 9  4  5  | 68  1   378 |
| 4   58  36  | 38 7  1  | 568 2   9   |
| 57  9   1   | 2  6  38 | 4   578 378 |
+-------------+----------+-------------+


I reached either this position or one very close. I looked for other ways to solve it because I had earlier read and commented about the 89 chain. Look at the strong links on 9 in rows 1 and 4. Either r1c1 or r4c3 must be a 9, therefore, r3c3 (and r6c1) cannot be a 9 and that solves the puzzle.
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jerry2007



Joined: 02 May 2007
Posts: 2

PostPosted: Wed May 02, 2007 12:53 pm    Post subject: please explain Reply with quote

Can you explain to me how you determined that R1C1 or R4C3 must be a 9? I just don't see it... Thank you
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Wed May 02, 2007 3:57 pm    Post subject: Re: please explain Reply with quote

jerry2007 wrote:
Can you explain to me how you determined that R1C1 or R4C3 must be a 9? I just don't see it... Thank you


Jerry,

Rows 1 and 4 each have only two possibilities for a 9. Both rows have one of the possibilities in column 6. Since both rows can't have their 9 in column 6, one of the two aforementioned cells must be a 9.

Hope this helps.
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Mesmin



Joined: 01 May 2007
Posts: 12
Location: Ontario

PostPosted: Wed May 02, 2007 4:11 pm    Post subject: Re: please explain Reply with quote

jerry2007 wrote:
Can you explain to me how you determined that R1C1 or R4C3 must be a 9? I just don't see it... Thank you


Row 1 has a nine in either Col 1 or 6;
Row 4 has a nine in either Col 3 or 6.

The pattern is almost an Xwing, and is called a skyscraper (this one is a skyscraper on its side).

The logic behind it is as follows: In Col 6, either Row 1 or Row 4 must be contain a 9, but we aren't sure which one. There are 2 other options for a 9 that see the 9s in Col 6. R1C1 and R4C3 (AKA Strong Links). One, and only one, of those cells must be a 9 (or the 9's in Col6 are invalidated). So any cells that see both R1C1 and R4C3 cannot contain a 9.
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Mesmin



Joined: 01 May 2007
Posts: 12
Location: Ontario

PostPosted: Wed May 02, 2007 4:14 pm    Post subject: Reply with quote

Beaten to the reply while I was typing. Serves me right for surfing the forums while at work.
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dulaby



Joined: 02 May 2007
Posts: 13

PostPosted: Wed May 02, 2007 5:43 pm    Post subject: Reply with quote

Here are the steps I used for this one:1-) there is an xy-wing on boxes 1 and 7 so that 7 is out of r3c1. 2-) after that an x-wing appears on columns 1 and 8(on 7) .Then you can choose several ways to complete it(assuming I am right...).
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jerry2007



Joined: 02 May 2007
Posts: 2

PostPosted: Wed May 02, 2007 5:47 pm    Post subject: Reply with quote

Thank you for the explanation.. It is a new technique I have learned today
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Emily



Joined: 12 Mar 2006
Posts: 1
Location: Vienna, Virginia

PostPosted: Thu May 03, 2007 1:22 pm    Post subject: Reply with quote

I solved this puzzle, but I'm not sure I did it correctly -- this was my first attempt trying to use any kind of Wing technique -- and would appreciate if someone would tell me. I apologize in advance for my lack of use of the more technically appropriate terms.

I reached the point noted above with the exception of the 6 in r4c2.

I used the 9s in r1c1 - r1c6 - r4c6 - r6c5 to eliminate the possibility of a 9 in r6c1.

That left me with the (1,7) pair in r6c1 and r6c2. That allowed me to fill in the 6 in r4c2, leaving me with (2,9) in r4c3 and r6c3 and (3,6,7) in the remainder of column 3, allowing me to fill in the 7 inn r3c3, and the rest of the puzzle came easily.

So my question, I suppose is, did I correctly eliminate the 9 in position r6c1 which allowed me to complete the puzzle, or did I just back into it?
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK

PostPosted: Thu May 03, 2007 3:13 pm    Post subject: Yet another way of doing it Reply with quote

I sometimes find that the "formal" solutions seem to be more suitable for computer programmes, rather than the loose creative thoughts that happen when I am on song. I personally hate to pencil in anything more than doublets

That being so - given the crunch point earlier (but without the 6 in r4c2) I was looking at col3 and observing that a seven in r3c3 would give the 2 and 9 in box 4 immediately - this happens if r4c6 is 9

BUT if r4c6 is 8 then r4c9 is 7, and if r4c6 is 9 then as described above r4c3 is 2 and so row 4 solves with r4c9 as 7

so r4c9 is 7 irrespective of whether r4c6 is 8 or 9.

so from here the solution falls out!

Incidentally Welcome back Forum after the long break!
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Thu May 03, 2007 4:48 pm    Post subject: Reply with quote

Emily wrote:

So my question, I suppose is, did I correctly eliminate the 9 in position r6c1 which allowed me to complete the puzzle, or did I just back into it?


Your logic looks O.K. to me! There are different ways to Rome (as well as Vienna). As Marty R pointed out, the use of those 9's (i.e. R1C1 or R4C3 must be a 9) eliminates the 9 in R3C3 directly - and also in R6C1. That you used the 17 pair to eliminate the 7's and then the 29 pair to eliminate the 9 in R3C3 is just another route in the same terrain.

Peter
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Thu May 03, 2007 4:54 pm    Post subject: Re: Yet another way of doing it Reply with quote

George Woods wrote:
I was looking at col3 and observing that a seven in r3c3 would give the 2 and 9 in box 4 immediately - this happens if r4c6 is 9

BUT if r4c6 is 8 then r4c9 is 7, and if r4c6 is 9 then as described above r4c3 is 2 and so row 4 solves with r4c9 as 7

so r4c9 is 7 irrespective of whether r4c6 is 8 or 9.


I think, if I understand you correctly, that this is just a different explanation of "my" approach (i.e. as I originally described at the beginning of this thread.

Peter
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David



Joined: 02 Jun 2006
Posts: 58
Location: Bedford, UK

PostPosted: Thu May 03, 2007 8:03 pm    Post subject: Reply with quote

Since we are discussing roads to Rome and Vienna.............. you can also solve the puzzle using strong links / colouring. So taking Marty's posting above, and focusing on the 9's; r4c6-r1c6-r1c1-r3c3 allows the elimination of 9 from r4c3 and hence forces the 9's in box 4 into row 6.
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Jeff



Joined: 06 May 2007
Posts: 46

PostPosted: Sun May 06, 2007 11:32 pm    Post subject: May 1 2007 Puzzle Reply with quote

I am stumped on the May 1 puzzle. Here is what I have. The Hint says that a 6 goes in Row 4 Col 2. I cannot figure how this can be. Mesmin on earlier post indicated that x-wing, xy wing, and naked pair would do it. I can't figure out where the x-wing is and of course I also can't find the xy and naked pair.

[/code]
59/2/8/35/1/39/7/6/4
6/3/4/58/2/7/9/58/1
179/157/79/6/89/4/358/38/2
3/67/2679/1/5/89/28/4/78
8/4/5/7/3/2/1/9/6
179/17/279/4/89/6/238/378/5
2/678/367/9/4/5/68/1/378
4/568/36/38/7/1/568/2/9
57/9/1/2/6/38/4/578/378

Could someone tell me how to write these number in the nice neat box as was done at the beginning of the discussion on the May 1 puzzle. I tried to find some instructions, but couldn't find any.

Many thanks.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Mon May 07, 2007 12:16 am    Post subject: Reply with quote

Jeff,

There are two good ways to post a properly aligned grid.

If you are doing a puzzle (regardless of puzzle source) online on this site, all you have to do is click the "Ascii" button to the right of the grid. Then follow the instructions in the pop-up window to copy and paste the grid into the message box.

Otherwise, type the grid into Notepad, which uses a fixed xx font, or into a word processing program, and choose a font that uses a fixed xx, such as Courier New. Proofread the grid before posting. Select (highlight) the grid and copy it (Ctrl+C). In the forum message box, click "Code", then paste (Ctrl+V) the grid to the right of the Code tag. Click "Code" again which inserts the tag at the end of the grid.

A properly aligned grid makes it easier for people to analyze your position and may well get you a quicker response.

This is an example of a grid which was first typed into Notepad. It takes less time than it looks like, as once you establish the maximum number of spaces per cell, you get into a rhythm and it takes less than five minutes.


Code:
-------------------------------------------------------------------
|23569  2369   1      |259    8      7      |2356   356    4      |
|23569  23689  2359   |1      24     49     |235678 35678  2358   |
|4      28     7      |25     3      6      |9      1      258    |
-------------------------------------------------------------------
|1239   4      239    |289    126    5      |368    3689   7      |
|123579 123579 6      |289    12     39     |4      3589   13589  |
|8      139    359    |7      146    349    |356    2      1359   |
-------------------------------------------------------------------
|27     5      8      |3      9      1      |27     4      6      |
|139    139    4      |6      7      2      |358    3589   3589   |
|23679  23679  239    |4      5      8      |1      379    239    |
-------------------------------------------------------------------
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Jeff



Joined: 06 May 2007
Posts: 46

PostPosted: Mon May 07, 2007 2:34 pm    Post subject: Reply with quote

I am stumped on the May 1 puzzle. I finally figured out how to put the numbers into a nice grid, thanks to some suggestions from the very knowledgeable group.

The hint states that a 6 should go in R4C2. In an earlier message "Mesmin" said that this comes about by "X-wing, XY wing, and then a naked pair". Could some one lead me through this. I don't see an X-wing anywhere, so I can't get to the XY or Naked pair.

Many thanks.

Code:

+--------------+----------+-------------+
| 59  2   8    | 35 1  39 | 7   6   4   |
| 6   3   4    | 58 2  7  | 9   58  1   |
| 179 157 79   | 6  89 4  | 358 38  2   |
+--------------+----------+-------------+
| 3   67  2679 | 1  5  89 | 28  4   78  |
| 8   4   5    | 7  3  2  | 1   9   6   |
| 179 17  279  | 4  89 6  | 238 378 5   |
+--------------+----------+-------------+
| 2   678 367  | 9  4  5  | 68  1   378 |
| 4   568 36   | 38 7  1  | 568 2   9   |
| 57  9   1    | 2  6  38 | 4   578 378 |
+--------------+----------+-------------+
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Mesmin



Joined: 01 May 2007
Posts: 12
Location: Ontario

PostPosted: Mon May 07, 2007 2:53 pm    Post subject: Reply with quote

Jeff,

From where you are you don't need the X-Wing. Just the XY and then the naked pair. Box1 is where you should be looking. If you need a more precise hint, let me know.

Perhaps I went a round about way with the X-Wing, and it isn't really required.
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