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alanr555
Joined: 01 Aug 2005
Posts: 198
Location: Bideford Devon EX39
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 Posted: Sun Dec 30, 2007 1:56 am Post subject: Dec 30th VH |
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Mandatory Pairs techniques resolved 25 cells - leaving another
25 to go, of which 21 were bi-value cells.
A W-wing resolved one more cell - after which the grading moved
from VH to Easy.
Along the way a potential unique rectangle was recognised.
With (abc/abc/ab/ab) in its corners a strong link on "c" was
indicated in order to avoid the DP. This enabled two eliminations
in the same line as the two corners involved. Subsequently the
rectangle became (ac/ac/ab/ab) and the peril was avoided!
I do not regard unique rectangles of that type as an advanced
technique and so include them in my Mandatory Pairs collection
but others may assess all UR avoidances as "advanced".
This was another good example of a VH which provides a plethora
of bi-value cells - making pattern spotting much easier. In fact the
elimination was from another bi-value cell as well and so reducing
as many cells as possible to bi-value status has a double benefit.
Details of the W-wing and identification of the UR are not given in
this post in view of the relatively recent release of the puzzle. |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Sun Dec 30, 2007 3:43 am Post subject: |
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x-wing on 3's
x-wing on 7's
then you can eliminate some naked pairs in box 5 I think
then
coloring on 6's |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Sun Dec 30, 2007 3:54 am Post subject: |
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| Code: | 2 1 8 | 56 567 4 | 3 9 r67
4 5 37 | 9 3r6 2 |g67 1 8
67 36 9 | 78 1 38 | 2 5 4
------------------------+-------------------------+------------------
69 4 2 | 78 78 5 | 1 3 g69
5 8 37 | 3g6 9 1 |r67 4 2
79 36 1 | 4 2 3r6 | 5 8 79
------------------------+-------------------------+------------------
8 2 6 | 35 35 9 | 4 7 1
3 7 4 | 1 r68 g68 | 9 2 5
1 9 5 | 2 4 7 | 8 6 3 |
this is after the x-wings on the 3's and 7's
the coloring in the grid kills all the red 6's since
6 in r2c5 is red and
6 in r8c5 is red
Last edited by storm_norm on Sun Dec 30, 2007 10:22 am; edited 1 time in total |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sun Dec 30, 2007 5:59 am Post subject: |
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| This was disappointingly easy. One simple coloring took out one 6 and that was it. |
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alanr555
Joined: 01 Aug 2005
Posts: 198
Location: Bideford Devon EX39
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| Posted: Sun Dec 30, 2007 9:27 am Post subject: |
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| storm_norm wrote: |
The coloring in the grid kills all the red 6's since
6 in r2c5 is red and
6 in r8c5 is red
This is after the x-wings on the 3's and 7's
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Thank you for this excellent example/explanation of colouring
on a single digit. It appears to be a particular form of the
implication chain - based on binary logic - but restricted to
STRONG links (so that it is "two-way") and a single digit.
One "colour" must be false, implying the other to be true.
However, I do not understand the x-wing references.
Using the Mandatory Pairs techniques, I had achieved the same grid
as Storm_Norm with the following exceptions
r1c4 has 567 rather than 56
r2c5 has 367 rather than 36
r3c4 has 378 rather than 78
I do not think that these eliminations would have got me very far
but I would like to know how they were achieved. Recently I
have had the xyz and xy wings explained in non-algebraic terms
and so now it is down to the ONE element pattern.
Region two contains 35678 in five unresolved cells.
What is the technique for simplifying that?
On what do the eliminations depend?
+++
As the grid is now revealed, I can say that my solution rested on
a potential unique rectangle in r4c4 to r6c9 (with 79 the danger)
and then a W-wing on r1c9/r5c7 linked by "6" in column four. This
allowed elimination of 7 from r2c7 (which, incidentally, is a "green"
in the colouring quoted previously). |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Sun Dec 30, 2007 10:27 am Post subject: |
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| Marty R. wrote: | | This was disappointingly easy. One simple coloring took out one 6 and that was it. |
agreed |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Sun Dec 30, 2007 10:36 am Post subject: |
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alanr555 wrote
| Quote: | r1c4 has 567 rather than 56
r2c5 has 367 rather than 36
r3c4 has 378 rather than 78 |
Alan,
it would be awesome if you could provide a full grid. then perhaps the answers you need can be given. |
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sdq_pete
Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL
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| Posted: Sun Dec 30, 2007 12:55 pm Post subject: |
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I always like to show the "X techniques"...
| Code: |
+-----------+------------+----------+
| 2 1 8 | 567 567 4 | 3 9 67 |
| 4 5 37 | 9 367 2 | 67 1 8 |
| 67 36 9 | 378 1 38 | 2 5 4 |
+-----------+------------+----------+
| 679 4 2 | 678 678 5 | 1 3 679 |
| 5 8 37 | 367 9 1 | 67 4 2 |
| 79 36 1 | 4 2 36 | 5 8 79 |
+-----------+------------+----------+
| 8 2 6 | 35 35 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+-----------+------------+----------+
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Play this puzzle online at the Daily Sudoku site
| Code: | X 7 C37
XY 368 R3C6 |
solves it.
Peter |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Sun Dec 30, 2007 2:55 pm Post subject: |
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At this point
| Code: | +-------------+-------------+-------------+
| 2 1 8 | 567 567 4 | 3 9 67 |
| 4 5 37B | 9 367 2 | 67C 1 8 |
| 67 36A 9 | 378 1 38 | 2 5 4 |
+-------------+-------------+-------------+
|679A 4 2 | 678 678 5 | 1 3 679C|
| 5 8 37 | 367 9 1 | 67c 4 2 |
| 79 36a 1 | 4 2 36 | 5 8 79 |
+-------------+-------------+-------------+
| 8 2 6 | 35 35 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+-------------+-------------+-------------+ |
There is a UR on <79> that takes out <6> in R4C45.
Or, there is a flightless XY-wing ABC in R23. You can color both pincers, to A and C in R4, to make the same eliminations as the UR.
This does not solve the puzzle, but I think it is an interesting move.
Keith |
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TexCat
Joined: 07 Jul 2006
Posts: 32
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| Posted: Sun Dec 30, 2007 2:55 pm Post subject: |
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| Code: |
+----------+-----------+---------+
| 2 1 8 | 56 567 4 | 3 9 67 |
| 4 5 37 | 9 36 2 | 67 1 8 |
| 67 36 9 | 78 1 38 | 2 5 4 |
+----------+-----------+---------+
| 69 4 2 | 78 78 5 | 1 3 69 |
| 5 8 37 | 36 9 1 | 67 4 2 |
| 79 36 1 | 4 2 36 | 5 8 79 |
+----------+-----------+---------+
| 8 2 6 | 35 35 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+----------+-----------+---------+
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Columns 4 and 7 form a skyscraper of 6's that eliminate 6 in R2C5. No crayons necessary. ; - } |
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Clement
Joined: 24 Apr 2006
Posts: 1113
Location: Dar es Salaam Tanzania
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| Posted: Sun Dec 30, 2007 4:40 pm Post subject: Daily Sudoku SUn 30-Dec-2007 |
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| XY-Wing {6,7}r5c7 as a Pivot and {3,7}r5c3;{3,6}r6c6 as pincers removing 3 in {3,6}r6c2 solves the puzzle. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sun Dec 30, 2007 4:52 pm Post subject: Re: Daily Sudoku SUn 30-Dec-2007 |
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| Clement wrote: | | XY-Wing {6,7}r5c7 as a Pivot and {3,7}r5c3;{3,6}r6c6 as pincers removing 3 in {3,6}r6c2 solves the puzzle. |
This is the grid from the post immediately preceding yours. Of the three cells you mention, there is no XY-Wing, as none of the cells can see the other two.
| Code: | +----------+-----------+---------+
| 2 1 8 | 56 567 4 | 3 9 67 |
| 4 5 37 | 9 36 2 | 67 1 8 |
| 67 36 9 | 78 1 38 | 2 5 4 |
+----------+-----------+---------+
| 69 4 2 | 78 78 5 | 1 3 69 |
| 5 8 37 | 36 9 1 | 67 4 2 |
| 79 36 1 | 4 2 36 | 5 8 79 |
+----------+-----------+---------+
| 8 2 6 | 35 35 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+----------+-----------+---------+ |
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Clement
Joined: 24 Apr 2006
Posts: 1113
Location: Dar es Salaam Tanzania
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| Posted: Sun Dec 30, 2007 4:58 pm Post subject: Daily Sudoku SUn 30-Dec-2007 |
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| XY-Wing {6,7}r5c4 as a Pivot and {3,7}r5c3;{3,6}r6c6 as pincers removing 3 in {3,6}r6c2 solves the puzzle. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sun Dec 30, 2007 6:13 pm Post subject: Re: Daily Sudoku SUn 30-Dec-2007 |
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| Clement wrote: | | XY-Wing {6,7}r5c4 as a Pivot and {3,7}r5c3;{3,6}r6c6 as pincers removing 3 in {3,6}r6c2 solves the puzzle. |
I'm just not understanding. I don't see a 67 in r5c4 nor do I see an XY-Wing in those cells. There is an XY-Wing on 37-36-67 pivoted in r5c3 with 6 as pincers, but they don't eliminate anything.  |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Sun Dec 30, 2007 7:03 pm Post subject: |
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In this position:
| Code: | +----------+-----------+---------+
| 2 1 8 |56@ -567 4 | 3 9 67 |
| 4 5 37 | 9 36@ 2 | 67 1 8 |
| 67 36 9 | 78 1 38 | 2 5 4 |
+----------+-----------+---------+
| 69 4 2 | 78 78 5 | 1 3 69 |
| 5 8 37 | 36 9 1 | 67 4 2 |
| 79 36 1 | 4 2 36 | 5 8 79 |
+----------+-----------+---------+
| 8 2 6 | 35 35@ 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+----------+-----------+---------+ |
I have marked an XY-wing that does make an elimination.
Keith |
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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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| Posted: Mon Dec 31, 2007 6:23 pm Post subject: |
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I used an Empty Rectangle solution that was simply elegant in its simplicity.
Using the previous grid, there are only two <6>s in R5. There's an ER or hinge for <6>s in Box 3. Thus, it doesn't matter which cell is the <6> in R5 ---- R1C4 cannot be a <6>.
Though I say it myself - a nice touch to the last VH of the year. |
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achievecn
Joined: 12 Sep 2006
Posts: 1
Location: China
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| Posted: Tue Jan 01, 2008 1:53 pm Post subject: |
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Thanks.
Daily sudoku. |
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Sue
Joined: 06 Jan 2008
Posts: 6
Location: Adelaide
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| Posted: Sun Jan 06, 2008 11:07 am Post subject: help needed |
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Can someone please help me with this puzzle. I've read all the previous posts, but don't understand what some of the terminologies mean. What would be my next step? The hint is that there is a 3 in row 7, column 4, but I don't know how to achieve this.
Thanks
2 1 8 | 567 567 4 | 3 9 67 |
| 4 5 37 | 9 367 2 | 67 1 8 |
| 67 36 9 | 3678 1 368 | 2 5 4 |
+-----------+--------------+----------+
| 679 4 2 | 678 678 5 | 1 3 679 |
| 5 8 37 | 367 9 1 | 67 4 2 |
| 679 36 1 | 4 2 36 | 5 8 679 |
+-----------+--------------+----------+
| 8 2 6 | 35 35 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+-----------+--------------+----------+ |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Sun Jan 06, 2008 2:48 pm Post subject: |
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In R6 there is a pair <36>, so you can eliminate these in the other cells to reveal another pair, <79>.
In B1, <6> only occurs in R3. You can eliminate <6> from all cells in B2R3. Leaving you here:
| Code: | +-------------+-------------+-------------+
| 2 1 8 | 567 567 4 | 3 9 67 |
| 4 5 37 | 9 367 2 | 67 1 8 |
| 67 36 9 | 378 1 38 | 2 5 4 |
+-------------+-------------+-------------+
| 679 4 2 | 678 678 5 | 1 3 679 |
| 5 8 37 | 367 9 1 | 67 4 2 |
| 79 36 1 | 4 2 36 | 5 8 79 |
+-------------+-------------+-------------+
| 8 2 6 | 35 35 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+-------------+-------------+-------------+ |
Look at C26. <3> appears only twice in each column, and they line up in the rows R36. If you think about it, <3> must be the solution on one of the diagonals of the rectangle R36C26. This is an X-wing. You can eliminate <3> in R3C4, because one of R3C26 must be <3>.
[Edit - This statement is incorrect: The only remaining <3> in C4 is R7C4.]
Continuing, there is an X-wing on <7> in C37. It takes out <7> in R2C5 and R5C4.
A pair <36> in B5 takes out <6> in R4B5.
Pairs <7> in R4 and C4 clear <7> from the other cells in R4 and C4. Leaving you here:
| Code: | +-------------+-------------+-------------+
| 2 1 8 | 56@ 567 4 | 3 9 67 |
| 4 5 37 | 9 36# 2 | 67 1 8 |
| 67 36 9 | 78 1 38 | 2 5 4 |
+-------------+-------------+-------------+
| 69 4 2 | 78 78 5 | 1 3 69 |
| 5 8 37 | 36 9 1 | 67 4 2 |
| 79 36 1 | 4 2 36 | 5 8 79 |
+-------------+-------------+-------------+
| 8 2 6 | 35 35@ 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+-------------+-------------+-------------+ |
This is a BUG+1. R1C5 must be <6>.
Or, I have marked an XY-wing as @#@. Any cell that sees both @ cells cannot be <5>. In particular, R7C4 must be <3>.
For help with terminology, do a Google search on "sudopedia". Also, Sudopedia has explanations of techniques like the BUG+1 I mentioned.
[End edit]
Best wishes,
Keith
Last edited by keith on Sun Jan 06, 2008 6:28 pm; edited 1 time in total |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sun Jan 06, 2008 4:43 pm Post subject: |
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Hi Sue, welcome to the forum.
| Quote: | | Code: | +-------------+-------------+-------------+
| 2 1 8 | 567 567 4 | 3 9 67 |
| 4 5 37 | 9 367 2 | 67 1 8 |
| 67 36 9 | 378 1 38 | 2 5 4 |
+-------------+-------------+-------------+
| 679 4 2 | 678 678 5 | 1 3 679 |
| 5 8 37 | 367 9 1 | 67 4 2 |
| 79 36 1 | 4 2 36 | 5 8 79 |
+-------------+-------------+-------------+
| 8 2 6 | 35 35 9 | 4 7 1 |
| 3 7 4 | 1 68 68 | 9 2 5 |
| 1 9 5 | 2 4 7 | 8 6 3 |
+-------------+-------------+-------------+ |
Look at C26. <3> appears only twice in each column, and they line up in the rows R36. If you think about it, <3> must be the solution on one of the diagonals of the rectangle R36C26. This is an X-wing. You can eliminate <3> in R3C4, because on of R3C26 must be <3>.
The only remaining <3> in C4 is R7C4. |
Keith, I just don't see it. What about the 3 in r5c4? What I'm seeing is the X-Wing on 7 in columns 3 and 7. The eliminations therefrom open up a 38-36-68 XY-Wing which will put the 3 in r7c4. |
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