The New Sudoku Players' Forum

[mike_r]

so i just started recently playing sudoku on my phone and i love it. i am stuck on this puzzle from the "technical" difficulty of Platinum Sudoku which is a sudoku game on my cell phone.

helpful suggestions are appreciated.

Code: Select all

19  27  18   |  5   6   389  | 38  4    27
679 5   26   |  4   38  29   | 1   38   27
3   4   28   |  28  7   1    | 9   6    5
_____________+_______________+______________
8   6   9    |  1   5   4    | 7   2    3
2   3   4    |  6   9   7    | 58  58   1
5   1   7    |  238 38  238  | 4   9    6
_____________+_______________+______________
76  8   3    |  9   1   56   | 2   75   4
176 27  1256 |  38  4   3568 | 53  1357 9
4   9   15   |  7   2   53   | 6   135  8


[mike_r]

original grid i believe

Code: Select all

 . . . | 5 6 . | . . .
 . 5 . | 4 . . | 1 . .
 3 . . | . . 1 | 9 6 .
_______+_______+______
 8 . . | . . 4 | . 2 3
 . . 4 | . 9 . | . . 1
 . 1 7 | . . . | . . .
_______+_______+______
 . 8 3 | . . . | . . 4
 . . . | . . . | . . .
 . . . | 7 2 . | 6 . .


[ArkieTech]

This is called a skyscraper. Removing a 3 from r1c6 solves your puzzle.
There is a problem with your original grid. Could you check it for typo's.

Code: Select all

 *-----------------------------------------------------------*
 | 19    27    18    | 5     6     89-3  | 38    4     27    |
 | 679   5     26    | 4    *38    29    | 1    *38    27    |
 | 3     4     28    | 28    7     1     | 9     6     5     |
 |-------------------+-------------------+-------------------|
 | 8     6     9     | 1     5     4     | 7     2     3     |
 | 2     3     4     | 6     9     7     | 58    58    1     |
 | 5     1     7     | 238   38    238   | 4     9     6     |
 |-------------------+-------------------+-------------------|
 | 67    8     3     | 9     1     56    | 2     57    4     |
 | 167   27    1256  | 38    4     3568  | 35    1357  9     |
 | 4     9     15    | 7     2    *35    | 6    *135   8     |
 *-----------------------------------------------------------*


[tarek]

This is called a skyscraper. Removing a 3 from r1c6 solves your puzzle.

I call it a sashimi finned x-wing

Code: Select all

 *-----------------------------------------------------------*
 | 19    27    18    | 5     6     89-3  | 38    4     27    |
 | 679   5     26    | 4    *38   *29    | 1    *38    27    |
 | 3     4     28    | 28    7     1     | 9     6     5     |
 |-------------------+-------------------+-------------------|
 | 8     6     9     | 1     5     4     | 7     2     3     |
 | 2     3     4     | 6     9     7     | 58    58    1     |
 | 5     1     7     | 238   38    238   | 4     9     6     |
 |-------------------+-------------------+-------------------|
 | 67    8     3     | 9     1     56    | 2     57    4     |
 | 167   27    1256  | 38    4     3568  | 35    1357  9     |
 | 4     9     15    | 7     2    *35    | 6    *135   8     |
 *-----------------------------------------------------------*

If this technique was required ... I wouldn't consider it suitable for a newbie ... so many building blocks are needed prior to this point. See the Ultimate Fish guide

[mike_r]

yeah i was reading up on the technique and it blew my mind. what's strange for me is the 3 previous ones i solved on the "technical" difficulty didn't require anything of this nature.

thank you for the assistance

[DonM]

I find it easier to see this as a skyscraper, mainly because if you are looking for patterns in general, it will be easier to simply look for 2 sets of conjugate pairs of the same number where 2 of the digits from each conjugate pair are in the same house (row, column or box). This might be called the floor of the pattern. Any digit of that value that sees both digits that are on the end opposite the floor can be removed. If the house where the 'floor' exists is a row or column, you have found a skyscraper; if a box, you've found a 2-string kite.

In other words, following this basic principle, you're really looking for one pattern rather than 3 (skyscraper, 2-string kite, sashimi x-wing). FWIW: having recently dedicated some time to going back and solving Mepham diabolicals to bone up on my basic (Pattern-A) pattern solving, I'm finding that skyscrapers & 2-string kites are very common in these puzzles.

[ronk]

original grid i believe

Code: Select all

 . . . | 5 6 . | . . .
 . 5 . | 4 . . | 1 . .
 3 . . | . . 1 | 9 6 .
_______+_______+______
 8 . . | . . 4 | . 2 3
 . . 4 | . 9 . | . . 1
 . 1 7 | . . . | . . .
_______+_______+______
 . 8 3 | . . . | . . 4
 . . . | . . . | . . .
 . . . | 7 2 . | 6 . .


Morphed to 180-degree rotational symmety ...

Code: Select all

 . . . | . . . | . 6 5
 . . 3 | . 6 9 | 1 . .
 . 5 . | . . 1 | . . 4
-------+-------+-------
 . . . | . . 6 | . 2 7
 . . . | . . . | . . .
 3 8 . | 4 . . | . . .
-------+-------+-------
 4 . . | 1 . . | . 9 .
 . . 8 | 3 2 . | 4 . .
 7 1 . | . . . | . . .

[tarek]

In other words, following this basic principle, you're really looking for one pattern rather than 3 (skyscraper, 2-string kite, sashimi x-wing). FWIW: having recently dedicated some time to going back and solving Mepham diabolicals to bone up on my basic (Pattern-A) pattern solving, I'm finding that skyscrapers & 2-string kites are very common in these puzzles.

The single pattern to me is the x-wing which would subsume all the above ....

the Sashimi Finned X-wing is a subdivision ....

if r2c6 had a 3 you could still make the same elimination as a Finned X-wing (again a subdivision of X-wing), you wouldn't be able to do it as a skyscraper ....

If you add prefixes to describe these subdivisions ...
Shape (configuration)
Fin status
Sashimi status

Then it will subsume all including degenerate X-wing ...

tarek

[DonM]

In other words, following this basic principle, you're really looking for one pattern rather than 3 (skyscraper, 2-string kite, sashimi x-wing). FWIW: having recently dedicated some time to going back and solving Mepham diabolicals to bone up on my basic (Pattern-A) pattern solving, I'm finding that skyscrapers & 2-string kites are very common in these puzzles.

The single pattern to me is the x-wing which would subsume all the above ....

the Sashimi Finned X-wing is a subdivision ....

if r2c6 had a 3 you could still make the same elimination as a Finned X-wing (again a subdivision of X-wing), you wouldn't be able to do it as a skyscraper ....

tarek

I understand what you're saying and I don't see either view as 'right or wrong' in the broad sense. A tutorial on these patterns would likely start with the logic behind the X-wing. However, when it comes to the pure visual process of finding these patterns (ie. what one is actually looking for), my guess would be that for most people (it's certainly true in my case), it is different for an X-wing pattern vs. the basic turbofish Skyscraper & 2-String Kite. In other words, the kite doesn't look anything like an X-wing and and combination of the skyscraper pattern & the placement of the 'elimination cell' doesn't look much like that of the X-wing either. (at least to my eyes ). Likewise, while as you say, if r2c6 had a 3 then you could still make the same elimination as Finned X-wing..., you wouldn't be able to do it as a skyscraper' , in that situation, I would pick up the elimination during my search for X-wings.

Again, this is the way I see it and the way I teach it to those who are trying to master basic puzzles (in the newspaper category). On the other hand, I am certainly aware that pattern solving is a very personal procedure: What I see as a skyscraper, others may prefer to see as a sashimi x-wing. I'm wondering whether this is a case where the theory and the actual practice somewhat diverge.

[tarek]

I am certainly aware that pattern solving is a very personal procedure: What I see as a skyscraper, others may prefer to see as a sashimi x-wing. I'm wondering whether this is a case where the theory and the actual practice somewhat diverge.

This is all open for discussion ....

I have been part of several discussions on the same topic ... In one of them the Skyscraper & 2-string kite were introduced

I believe from a visual point of view, It was then better described as 2 strong links , 3 strong links ... which to me is the easiest visual aid following that path (Mike Barker has them this way in his solver IIRC).

tarek

[DonM]

I have been part of several discussions on the same topic ... In one of them the Skyscraper & 2-string kite were introduced

tarek

Yes I know. I tend to think of the 'visual aid' Havard provided was along the lines I'm talking about- an alternative to seeing these patterns as visual derivatives of X-wings or there subsets (sashimi, finned etc.).

In fact, they (skyscrapers, kites) work better for me than other descriptions of the same or similiar patterns: broken wings, guardians and the like.