The New Sudoku Players' Forum

[Jacky]

After using all the methods I could and using the skyscraper method I just learned, I believe I am stuck again.

[Leren]

Code: Select all

*------------------------------------------------------------------------*
| 45      8      6       | 7      2      459     | 3      459    1       |
| 2457    9      257     | 3      1      45      | 6      245    8       |
| 2345    34     1       | 456    8      4569    | 459    7      259     |
|------------------------+-----------------------+-----------------------|
| 6      #37    *58      | 9      4      1       | 578    235    257     |
|#134-89 #347   *89      | 26     5      26      | 1789   39     79      |
|#1-259  *25    *259     | 8      3      7       | 159    6      4       |
|------------------------+-----------------------+-----------------------|
| 5789    1      5789    | 45     6      3       | 2      459    579     |
| 257     6      4       | 25     9      8       | 57     1      3       |
| 259     25     3       | 1      7      245     | 459    8      6       |
*------------------------------------------------------------------------*

Leren to the rescue again !

You probably know this move but have missed it. There is a naked quad (2589) in the 4 cells marked * in Box 4.

You can remove 2589 from other cells in Box 4, which solves r6c1 and the puzzle.

That is some humungous diagram. Here is the puzzle solved cell status in line format : .8672.3.1.9.31.6.8..1.8..7.6..941.......5.......837.64.1..632...64.98.13..317..86

Leren

PS I just realized that, because there is a solved cell in Box 4, there is a complementary pattern - a hidden quad (1347) in the cells marked #, which gives the same eliminations.

Normally I'd quote the naked or hidden pattern with the smallest number of cells, but in this case they are the same. It's up to you to decide which is easier to see.

Leren

[JasonLion]

I always have problems spotting locked quads, so I would probably use the Finned Sashimi X-Wing in rows 6 and 7, columns 3 and 9. R12C6 is the fin, and R3C6 doesn't contain a 4 so it is sashimi. Anyway, that eliminates the 4 in R3C4, which lets you place a 4 in R7C4. This still leaves some work to do, so it isn't nearly as elegant as Leren's approach, and Finned Sashimi X-Wings are much more difficult to understand than locked quads, but I do find them much simpler to spot compared to quads, and this way no quads will be required.

[Leren]

Hi Jason, you must have mis-located that XWing, since Columns 3 and 9 have solved 4's.

To try and rescue the confusion I looked for a Sashimi XWing in 4's and found the following :

Code: Select all

*-----------------------------------------------------------------------*
| 45     8      6       | 7      2      459     | 3      459    1       |
| 2457   9      257     | 3      1      45      | 6      245    8       |
| 2345   2345   1       |*456    8      4569    |*459    7      259     |
|-----------------------+-----------------------+-----------------------|
| 6      357    58      | 9      4      1       | 578    235    257     |
| 13489  347    89      | 26     5      26      | 1789   39     79      |
| 1259   25     259     | 8      3      7       | 159    6      4       |
|-----------------------+-----------------------+-----------------------|
| 5789   1      5789    |f45     6      3       | 2      459    579     |
| 257    6      4       | 25     9      8       | 57     1      3       |
| 259    25     3       | 1      7      25-4    |*459    8      6       |
*-----------------------------------------------------------------------*

Sashimi Finned XWing in 4's c47 r39 with a fin Cell r7c4. For Jacky's benefit the three X Wing cells are marked * and the fin cell is marked f. The X Wing is Sashimi since there is no 4 in r9c4.

Neverthless you can eliminate the 4 in r9c6 and solve the puzzle that way, avoiding the quads.

However you might notice something about the 3 X Wing cells and the fin. They form a Skyscraper ! (Which you learned about last time). In fact all Sashimi Finned XWings are Skyscrapers !!

So you won't have to learn about Sashimi finned fish, which is a somewhat more involved topic, at this stage.

Leren

[Jacky]

Oh my,

I've only been using a limited form of the skyscraper. I never accounted for that use, but you're right that does make a lot of sense. Is that called X Wing Sashimi ?

I don't know how my Sudoku app progresses, but I've never encountered quads yet. I have only thought about trips for a while (e.g 2-5, 2-8, 5-8). Thanks guys for your quick responses!

[Leren]

The X Wing is called Sashimi because one of the four X Wing digits is missing - in this puzzle there is no 4 in r9c4. Even if it was there you would have a normal Finned X Wing and the elimination would still be valid.

Only finned XWings can be Sashimi, because otherwise one of the defining rows or columns would have only 1 X Wing digit and would be solved for that digit!

There is an article on Finned X Wings (Normal and Sashimi) here, an article on naked pairs, triples and quads here and one on hidden pairs, triples and quads here.

The Skyscraper view of the Sashimi finned X Wing is the same type that you found in your previous inquiry, it's just an upside down one.

You should be aware that any pattern can be rotated thru 90, 180 or 270 deg and still work in the right circumstances.

I had to look up what Sashimi actually meant. Apparently it's raw fish cut into thin slices !

Leren

[eleven]

Code: Select all

*-----------------------------------*
|  .  8  6  |  7  2  .  |  3  .  1  |
|  .  9  .  |  3  1  .  |  6  .  8  |
|  .  x  1  |  .  8  .  |  . *7  .  |
-------------------------------------
|  6  .  X  |  9  4  1  |  .  .  .  |
|  .  .  X  |  .  5  .  |  .  .  .  |
|  X  X  X  |  8 #3 #7  |  .  6 #4  |
------------------------------------
|  .  1  .  |  .  6  3  |  2  .  .  |
|  .  6 #4  |  .  9  8  |  .  1  3  |
|  .  x #3  |  1 *7  .  |  .  8  6  |
*-----------------------------------*

There is a hidden triple 347 in r4c2,r5c12, and it is not hard to spot, once you have seen that 7 is locked to r45c2.