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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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 Posted: Fri Sep 21, 2007 2:33 pm Post subject: Sept 21 VH |
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A w-wing, an xy-wing, and an x-wing did it for me.
Earl |
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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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| Posted: Fri Sep 21, 2007 2:47 pm Post subject: |
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| I like ERs cos I find patterns easier to spot than nos (eg xy & w wings). By my reckoning there are two ERs for 2s. One in C36 that gets rid of the 2 in R5C3 and another in C15 that rids the 2 in R4C1. That leaves an x-wing (another easy to spot pattern) that rids the 2 from R9C1. |
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Johan
Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium
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| Posted: Fri Sep 21, 2007 3:02 pm Post subject: |
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| An xy-wing and an x-wing opened the puzzle for me, nevertheless it was a naked quad or a naked pair that helped me in the initial phase of the puzzle, for reaching the final two steps solving the grid. |
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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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| Posted: Fri Sep 21, 2007 3:13 pm Post subject: Sept 21 VH |
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Cgordon,
It might help some of us if you would show the details of your solution with ER's.
Earl |
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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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| Posted: Fri Sep 21, 2007 3:14 pm Post subject: |
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| Quote: | | nevertheless it was a naked quad or a naked pair that helped me in the initial phase of the puzzle |
For some reason, it took me forever to spot that naked quad - which I seem to recall was in C9. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Fri Sep 21, 2007 3:35 pm Post subject: |
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| I used an XY-Wing and coloring on 2. I probably missed something because I don't believe coloring is needed to solve these puzzles. |
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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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| Posted: Fri Sep 21, 2007 4:12 pm Post subject: |
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I aint too good at posting grids (can't get nos to line up)- but I'll try to show the 2's I had available
[ | Code: |
+-------+-------+-------+
| . . 2 | . 2 . | . . . |
| 2 . . | . . 2 | . . . |
| . . . | . . . | . . . |
+-------+-------+-------+
| 2 2 2 | . 2 . | . . . |
| 2 . 2 | . . 2 | . . . |
| . . . | . . . | . . . |
+-------+-------+-------+
| . . . | . . . | . . . |
| . 2 2 | . . . | 2 . . |
| 2 . . | . . . | 2 . . |
+-------+-------+-------+
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[
There are two 2s in col 6. If R5C6 is the 2, R5C3 cannot be a 2. Alternately, if R2C6 is the 2, then because there is a T shaped hinge in box 1 (the top bit of the T in C3 is missing but I dont think that matters) R5C3 is still not a 2.
Similarly if you look at the two 2s in C5. If R4C5 is the 2, R4C1 cannot be a 2. And if R1C5 is the 2, then because there's an L shaped hinge in box 1 (with a bit missing), the R4C1 can still not be a 2.
Geez - I hope I got that right. Embarrasing if I didn't. |
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Johan
Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium
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| Posted: Fri Sep 21, 2007 4:37 pm Post subject: |
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| Quote: |
For some reason, it took me forever to spot that naked quad - which I seem to recall was in C9. |
cg,
You're right about C9, the [56] pair in Box 6 catched my eye (after my grid was covered with pencil marks and didn't see any other step, for cleaning up my grid)
The [56] pair could only reside in R2C9 and R8C9, which pins the <9> in C8 in Box 3. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Fri Sep 21, 2007 6:01 pm Post subject: |
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After basic steps...
in this position
| Code: |
+--------------------------+--------------------------+--------------------------+
| 1 9 26 | 5 26 4 | 8 3 7 |
| 28 7 5 | 3 1 28 | 4 9 6 |
| 468 46 3 | 7 68 9 | 5 1 2 |
+--------------------------+--------------------------+--------------------------+
| 2479 24 1248 | 6 278 3 | 17 5 489 |
| 247 3 1248 | 9 5 28 | 17 6 48 |
| 679 5 68 | 4 78 1 | 3 2 89 |
+--------------------------+--------------------------+--------------------------+
| 5 8 7 | 2 3 6 | 9 4 1 |
| 3 246 246 | 1 9 7 | 26 8 5 |
| 26 1 9 | 8 4 5 | 26 7 3 |
+--------------------------+--------------------------+--------------------------+
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one color wing on "2":
91-21=13-15=26-56=45-42=82-91
leaves 6 in r9c1 and the rest is all singles... |
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eddieg
Joined: 12 Jan 2006
Posts: 47
Location: San Diego, CA USA
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| Posted: Fri Sep 21, 2007 8:25 pm Post subject: |
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| Code: |
+---------------+----------+----------+
| 1 9 26 | 5 26 4 | 8 3 7 |
| 28 7 5 | 3 1 28 | 4 9 6 |
| 468 46 3 | 7 68 9 | 5 1 2 |
+---------------+----------+----------+
| 24789 24 148 | 6 278 3 | 17 5 489 |
| 2478 3 148 | 9 5 28 | 17 6 48 |
| 6789 5 68 | 4 78 1 | 3 2 89 |
+---------------+----------+----------+
| 5 8 7 | 2 3 6 | 9 4 1 |
| 3 246 246 | 1 9 7 | 26 8 5 |
| 26 1 9 | 8 4 5 | 26 7 3 |
+---------------+----------+----------+
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Play this puzzle online at the Daily Sudoku site
Okay, I am stuck right here. I don't know nothing about 'colouring' and such. Looking for straighforward approach to get me there. |
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Fri Sep 21, 2007 8:29 pm Post subject: |
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next step is: 8 in col 1 is confined to box 1
still not quite the solution though.
no "straightforward" approach.
sorry.
s why it's "very hard" probably.
Earl and Johan were talking about xy wings and stuff if you dont like coloring |
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nataraj
Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
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| Posted: Fri Sep 21, 2007 8:59 pm Post subject: |
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okay, I'll offer one more.
in your grid there seems to be a swordfish in cols 235 and this animal removes "2"s from rows 4,8 in particular r8c7. |
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Asellus
Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
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| Posted: Fri Sep 21, 2007 10:58 pm Post subject: |
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cgordon,
Regarding your <2> eliminations, both of them are Empty Rectangle (ER) eliminations, as I believe you were suggesting.
In the first case, the ER is due to there being no <2> candidates in the four cells R13C12. <2>s could be present in any of the other cells and this elimination would still be valid. (By the way, the R5C3 elimination creates a useful X-Wing in R25 in this case since there aren't any <2>s in R2C23.)
In the second case, the ER is due to there being no <2> candidates in R23C23. (The R4C1 elimination can also be seen as simple coloring of the C5-R1-B1 strong links, or as a result of the Finned X-Wing in R25.)
This is a nice example of how an offset pair within a Box can provide two different ERs.
As an aside, I don't spot ERs by looking for the "empty" pattern. Personally, I find it easier to see that the candidates are restricted to one row segment and one column within the Box. This also helps to see quickly how the ER "aims" its effects. With the 2-cell Box 1 ER in this example, one can see the segments as either R1 and C1 or as R2 and C3. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Fri Sep 21, 2007 11:02 pm Post subject: |
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| Eddie, I don't know if W-Wings are straightforward, but there is one on the 26 pairs in r1c3 and r9c1 which will take you a long way towards the solution. |
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Asellus
Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
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| Posted: Fri Sep 21, 2007 11:19 pm Post subject: |
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nataraj's "Color Wing" (or "Multi-Coloring") might be easier to picture this way:
| Code: | +-----------------+------------+----------+
| 1 9 2g6 | 5 2r6 4 | 8 3 7 |
| 2r8 7 5 | 3 1 28 | 4 9 6 |
| 468 46 3 | 7 68 9 | 5 1 2 |
+-----------------+------------+----------+
| 2479 B2R4 1248 | 6 B2g78 3 | 17 5 489 |
| 247 3 1248 | 9 5 28 | 17 6 48 |
| 679 5 68 | 4 78 1 | 3 2 89 |
+-----------------+------------+----------+
| 5 8 7 | 2 3 6 | 9 4 1 |
| 3 2G46 246 | 1 9 7 | 26 8 5 |
|#-26 1 9 | 8 4 5 | 26 7 3 |
+-----------------+------------+----------+ |
The weak link "bridge" is marked "B". The coloring of one branch of the wing is capitalized, the other lower case. Since the "bridge" is R-g, eliminations occur with r-G, as seen in the target cell marked #.
Many folks seem to feel that coloring is too complex or difficult. However, I find things such as this case to be easy to spot without making any color marks at all... easier to spot than most "fish" other than X-Wings, for instance. However, there is a "trick"...
I think of the two "bridge" cells as the same color. Let's say "red". Then, I look for a "green" cell from each "wing" chain to serve as pincers. Done this way, the lower case colors in the grid above are reversed and the elimination is done by "g-G". If the chains are short, as here, then it is easy to do in ones head with only a little practice.
Had you been searching for a Skyscraper on <2>s, you probably would have noticed the strong links in C2 and C5 branching in opposite directions from R4. Useless for a Skyscraper, they have potential for a "Color Wing" if at least one of them can be extended. Here, it is easy to see that the C5 link can be extended via R1 anb B1. It's just a matter of mentally fixing R8C2 as "green" then mentally "counting" red-green-red-green along the other chain and, Voilą!, "pincers". No marking is required.
This way of seeing a "Color Wing" or "Multi-Coloring" comes from Ruud's Sudocue.net guide, if not other places. |
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eddieg
Joined: 12 Jan 2006
Posts: 47
Location: San Diego, CA USA
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| Posted: Sat Sep 22, 2007 12:04 am Post subject: Thank You |
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Marty,
Thanks for the tip on the W-Wing. I have seen those described a few times and with a little research I now have the concept.
I will examine the post by Asellus a little later after taking care of family obligations, etc. |
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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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| Posted: Sat Sep 22, 2007 1:10 am Post subject: |
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| Quote: | | I don't spot ERs by looking for the "empty" pattern. Personally, I find it easier to see that the candidates are restricted to one row segment and one column within the Box. |
Asellus: Yes I definitely agree (at least I think I do). I also DON'T look for the "empty pattern" - in fact I think the term "empty rectangle' is rather inappropriate since it refers to the properties within one corner box rather than the macro rectangle formed in rows and cols. Some term with hinge would be better.
Nevertheless, when looking in the "empty rectangle" box - I find it easier to look for shapes of T, + or L, rather than its empty components. |
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TKiel
Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI
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| Posted: Sat Sep 22, 2007 12:59 pm Post subject: |
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| cgordon wrote: | | ...in fact I think the term "empty rectangle' is rather inappropriate...Some term with hinge would be better. |
How ironic. |
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cgordon
Joined: 04 May 2007
Posts: 769
Location: ontario, canada
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| Posted: Sat Sep 22, 2007 6:46 pm Post subject: |
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why's zat |
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