The New Sudoku Players' Forum

[MCC]

tso, you asked for 3x3 swordfish, I found one in this topic here.

MCC

[tso]

tso, you asked for 3x3 swordfish, I found one in this topic here.

Code: Select all

 
*--------------------------------------------------------------------*
 | 67    -789    1      | 4689   2      4689   | 478    5      3      |
 | 37     4      89     | 5      39     1      | 278    289    6      |
 | 36     2      5      | 7      369    4689   | 48     89     1      |
 |----------------------+----------------------+----------------------|
 | 124   +579    6      | 239    8     +579    | 23     123   +247    |
 | 24    +578    3      | 26     1     +567    | 9      268   +2478   |
 | 12    +789    89     | 2369   4     +679    | 5      12368 +278    |
 |----------------------+----------------------+----------------------|
 | 5      136    4      | 1689   69     2      | 368    7      89     |
 | 8      16     7      | 169    5      3      | 26     4      29     |
 | 9      36     2      | 468    7      468    | 1      38     5      |
 *--------------------------------------------------------------------
*

To catch a 9-cell Swordfish, it must make an exclusion -- and this one does -- if we squint a little. Though the 7 in r1c2 could be removed by locked candidates in box 4, no one can tell us that we can't removed it because of the 9-cell swordfish in 7s marked with plus signs.

[ronk]

To catch a 9-cell Swordfish, it must make an exclusion

I think there are two schools of thought on that: 1) as you state, and 2) that a pattern is a pattern whether or not it leads to an exclusion.

Personally, I'm in the 2nd camp.

Ron

[TKiel]

I found one also, which was in a puzzle generated by Simple Sudoku.



Tracy

[tso]

We have a winner! Not only does this have a 9-cell swordfish that DOES move the puzzle forward, there are no simpler tactics (pairs, trips, x-wing, unique rectangles, locked sets, singles) available. BONUS -- there are TWO swordfish in 3's at the same time -- and they make different exclusions.

Could you post the original puzzle?

Code: Select all

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


Code: Select all

 *--------------------------------------------------*
 | 9    6    5    | 7    134  48   | 18   38   2    |
 | 4    2    13   | 18   139  6    | 189  7    5    |
 | 13   8    7    | 5    2    39   | 4    369  136  |
 |----------------+----------------+----------------|
 | 136  9    8    | 4    7    23   | 126  5    136  |
 | 7    4    23   | 6    5    1    | 29   39   8    |
 | 136  5    123  | 39   8    239  | 7    4    136  |
 |----------------+----------------+----------------|
 | 2    1    4    | 39   39   5    | 68   68   7    |
 | 8    3    9    | 2    6    7    | 5    1    4    |
 | 5    7    6    | 18   14   48   | 3    2    9    |
 *--------------------------------------------------*


Elusive 9-cell swordfish in colums 1, 6 and 9.
Additional 6-cell swordfish in rows 1, 2 and 5.
Exclusions marked with 'x'.

Code: Select all

 *--------------------------------------------------*
 | .    .    .    | .   *3*   .    | .   *3*   .    |
 | .    .   *3*   | .   *3*   .    | .    .    .    |
 |[3]   .    .    | .    .   [3]   | .   x3   [3]   |
 |----------------+----------------+----------------|
 |[3].  .    .    | .    .   [3]   | .    .   [3]   |
 | .    .   *3*   | .    .    .    | .   *3*   .    |
 |[3].  .   x3    |x3    .   [3].  | .    .   [3]   |
 |----------------+----------------+----------------|
 | .    .    .    | 3   x3    .    | .    .    .    |
 | .    .    .    | .    .    .    | .    .    .    |
 | .    .    .    | .    .    .    | .    .    .    |
 *--------------------------------------------------*


r3c8 and r6c3 excluded by both swordfish
r6c4 excluded by 9-cell
r7c5 excluded by 6-cell

[TKiel]

I don't think so. I thought I had saved the puzzle but the only thing I could find that I had saved was the image. I'll keep looking and any suggestions on how/where to look would be appreciated. Anybody have a solver that runs in reverse?


Tracy

[vidarino]

I don't think so. I thought I had saved the puzzle but the only thing I could find that I had saved was the image. I'll keep looking and any suggestions on how/where to look would be appreciated. Anybody have a solver that runs in reverse?


Tracy

I do, actually, but when I tried "trimming" this one, the Swordfish situation disappeared, and I ended up with something with another solution path (including a Jellyfish with 3s, so maybe it's related.) I'll give it a few more trials, though, and see what I can come up with.

Edit: I found one starting position that appears to lead up to the 9-cell swordfish;

Code: Select all

9.5.....2
.....6.7.
.8.5..4..
.98.7....
7..6.1..8
....8.74.
.14..5...
.3.2..5..
5.....3.9


It's not perfectly symmetrical, so I have a rather strong feeling that it's not the original puzzle, but it seems to do the trick. Feel free to look for permutations that work better.

[wkrfresno]

This one has a jellyfish and a swordfish in 4s:

Code: Select all

6..5.298.
.5..38.26
..8..65..
9..3856..
86...7.35
531624897
...85..6.
.16279.58
.8546...9

[TKiel]

TKiel wrote:

I don't think so. I thought I had saved the puzzle but the only thing I could find that I had saved was the image.

Well, I think I figured it out, thanks to vidarino's post above and a bit of trial & error. The origional puzzle looked like this:

Code: Select all

 
 965.....2
 .2...6.7.
 ...5..4..
 .98.7....
 7..6.1..8
 ....8.74.
 ..4..5...
 .3.2...1.
 5.....329