The New Sudoku Players' Forum

[QBasicMac]

Here is how far I got:
<code>
-49 --- --5
-51 -98 3--
386 --- 921
825 -49 -1-
694 8-1 25-
173 562 -9-
537 --- 1-9
4-2 9-- 57-
9-8 --- -32

27 - - 1236 123 36 678 68 678
27 - - 26 27 467 467 46 467
7 - - 47 57 457 47 4 47
- - - 37 37 37 67 6 367
- - - 37 37 37 7 - 37
- - - - - - 48 48 48
- 6 - 246 28 46 468 468 468
- 16 - 136 138 36 68 68 68
- 16 - 1467 157 4567 46 46 46
</code>

I can't see any next move.

Mac

[tso]

You seem to have posted to unrelated puzzles -- the candidate lists don't correspond to anything in the puzzle grid.

(You need to deselect "Disable BBCode in this post" for "code" to work.)

Code: Select all

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


1) There are only three cells in row 3 left and they're all in box 2. They must contain a 4, 5 and 7 in some order -- so 4, 5 and 7 cannot be in another other cell in box 2. This is a naked triple.

2) After that, you'll find a naked pair in one of the columns. That should be enough to finish the puzzle quickly.

[QBasicMac]

Thanks for the reply, tso

Right, I posted values which showed pencilmarks where solution has already been found. Here is my corrected box 2
1236 123 36
26 - -
47 57 457

As you can see, I already eliminated 457 from the box. But I don't see what you are referring to as the next move.

Mac

[QBasicMac]

Never mind, tso, I see it now.

Just a general question (you are not the only one):

Why do you guys always reply so cryptically?

Why not just say "r1c6 and r8c6 each have candidates 3 and 6, thus all other cells in column 6 cannot have either 3 or 6?"

Or, to use jargon, "r1c6 and r8c6 are a naked pair, thus eliminating 3 and 6 from other cells in column 6"

Something like that would be more helpful.

But not to byte the hand that feeds me, thanks very much. I simply did not see those two cells had the same candidates.

That was the problem that had me stumped for a day.

Mac

[tso]

It's not always obvious how much of a hint someone wants. If you spell it out exactly -- it's not so much a hint as the solution.

[goldie5218]

hi all, i am looking for help from someone who understands swordfish - can manage x wings ok as well as all the other basic methods to reduce candidates - now trying to improve my solving techniques so thought i should give swordfish a go - ok first of all the tutorial on SadMan software Suduko says "look for 3 cols with ONLY TWO candidates for a given digit -if these fall on exactly 3 common rows, and each of these rows have at least 2 candidate cells then you have an swordfish!"
however on www.angusj.com it says " the swordfish is formed by 3 rows each with NO MORE than 3 cells with the specific candidate, and ALL sharing the same 3 columns ( and obviously i assume the reverse applies for the "column" swordfish " ?) --- a little confusing to me ,cannot understand the phrasing, do i look for three 2 or 3 candidates and how will i know which candidates i can erase? i find the explanation for the xwings to be clear and can navigate my way around them ok, but stuck on the swordfishes as i dont seem to be able to find/identify them correctly - any help will be much appreciated cheers goldie
,

[SteveF]

I doubt that this will totally fulfill your requirements, but at little bit of history may help the understanding.


When the swordfish was first put forward the definition was as per Simes (Sadman) that you quote. Thus it was thought that three columns (or rows) could only have two candidates each.

Later on someone put forward a new, less restrictive definition that still held good (appologies to whoever that was, I can't now remember but I suspect the details are somewhere in this forum).

This held that each of the three columns (or rows) could hold upto 3 candidates, as long as those three candidates fall into the three common rows (or columns). This is what angusj refers to.

By way of an example:

. . . . . . . . .
B. . A. . A. .
. . . . . . . . .

A. . A. . B. .
. . . . . . . . .
. . . . . . . . .

A. . B. . A. .
. . . . . . . . .
. . . . . . . . .

Consider that the A's and B's represent the only places that a candidate can go in columns 1, 4, 7.

The A's represent an example of the original 2 candidates per column definition. The B's represent where the extras can go in the 3 candidates per column definition.

If you have the above shape then you can remove any other occurrences for the candidate in rows 2, 4, 7.

[QBasicMac]

Hi, tso,

Well, this thread has been hijacked! LOL - I don't care - This is my last post in this thread.

Anyway, I see my question "I can't see any next move." was too vague. In the future, I will spell it out in more detail (plus get my pencilmarks right)

I'm sure this will make it more clear: "Please supply a detailed, exact solution, not a hint, that leads to the next candidate that can be eliminated."

Thanks again for the help, even though I am embarrassed that I couldn't see that pair.

Mac

[goldie5218]

sincere apologies to QbasicMac for hi jacking his forum - blame my bad manners on a lack of pc skills please - do not mean to be rude - thanks stevef for your reply - i can see that a three candidate version could also work but my original comment was that there is/are two methods to identify a swordfish? which is the correct version? or are they both correct? or should i be looking for " up to three candidates " ???
please clarify - cheers goldie

[angusj]

which is the correct version? or are they both correct? or should i be looking for " up to three candidates " ???
please clarify

They are both correct in that they will both find swordfish. However, the 'three candidate version' will find all swordfish while the other will find only a subset.

[Karyobin]

Sorry Goldie, I'm not going to assist you in any way other than to say I have never found, nor needed to find, a Swordfish.

A Swordfish, in my opinion, is a construct derived from the logic of X-wings. As such, it is an utterly correct logical structure. It seems to me the situation is (not particularly) analogous to deriving lines from points, squares from lines, cubes from squares and Tesseracts from cubes. But that doesn't mean I am ever going to actually find a tesseract (unless I watch certain, rather gruesome, films). So just because something can be proved to exist, doesn't necessarily mean you are going to find it. Whilst the swordfish itself is not limited to higher dimensions, they are extremely rare (I've been dabbling with sudoku since last March and the only times I've ever happened upon one there was invariably a simpler construct which negated the use of the swordfish in the first place).

From looking at the postings around here, I'd definitely recommend developing familiarity with Turbot fish, which seem to be far more common and easier to locate.

But that's just my opinion.

[goldie5218]

thanks very much angusj, will stick to the three candidate version from now on - hey Karobin, thanks for your comments as well - perhaps i didnt make myself clear to you - i like to do the puzzles on the simple suduko website and there they give puzzles that require swordfishes to solve them - now that i have been given the hint as to how to identify them i cant wait to try and solve them - have been successful in solving all the xwing examples on the same site so now need to 'kill' the swordfish examples to try and improve my solving skills! yes! and just when i thought it was ok to go back into the water, i find there is a thing called a 'turbot fish ' just waiting for me??? sorry to be such a cluck but could you either explain/describe the animal to me ? or point me in the right direction and i can confuse myself? really appreciate how you guys are prepared to help the 'battlers' cheers goldie

[tso]

Sorry Goldie, I'm not going to assist you in any way other than to say I have never found, nor needed to find, a Swordfish.

Just because a swordfish might be rare "in the wild", that is, in a puzzle generated at "random", doesn't mean that one cannot create unlimited puzzles that contain swordfish at will. For example Simple Sudoku's Extreme contain at least one Swordfish by design. I like finding Swordfish. Like it's name sake, you are right, you're not likely to find it at random anywhere you look -- but somehow, I manage to find a piece to grill for dinner least once a week.

Also, the methods that can be used to generate a puzzle at "random" are diverse enough to make many patterns as rare or common as one wishes. Furthermore, it seems obviou ... *ouch* ... what the heck did I just sit on ... wha? ... crud, I've got to clean these tesseracts out of this couch ... I gotta go, I think my hip is bleeding ... gol durn 4th dimension.

[Ocean]

Just because a swordfish might be rare "in the wild", that is, in a puzzle generated at "random", doesn't mean that one cannot create unlimited puzzles that contain swordfish at will. For example Simple Sudoku's Extreme contain at least one Swordfish by design. I like finding Swordfish. Like it's name sake, you are right, you're not likely to find it at random anywhere you look -- but somehow, I manage to find a piece to grill for dinner least once a week.

Also, the methods that can be used to generate a puzzle at "random" are diverse enough to make many patterns as rare or common as one wishes...

I think there are lots of other Exclusion Patterns, more or less similar to the Swordfish. Here is just one example:

Code: Select all

  Grid:             Pattern:          Reduction:
 *-----------*     *-----------*     *-----------*
 |.1.|.1.|..1|     |.X.|.X.|..X|     |.1.|.1.|..1|
 |.1.|1..|..1|     |.X.|X..|..X|     |.1.|1..|..1|
 |111|111|111|     |...|...|...|     |1.1|..1|11.|
 |---+---+---|     |---+---+---|     |---+---+---|
 !111|111|111|     |...|...|...|     |1.1|..1|11.|
 |111|111|111|     |...|...|...|     |1.1|..1|11.|
 |.1.|11.|..1|     |.X.|XX.|..X|     |.1.|11.|..1|
 |---+---+---|     |---+---+---|     |---+---+---|
 |111|11.|111|     |...|..0|...|     |1.1|11.|11.|
 |111|11.|111|     |...|..0|...|     |1.1|11.|11.|
 |111|11.|111|     |...|..0|...|     |1.1|11.|11.|
 *-----------*     *-----------*     *-----------*

The swordfish is probably overrepresented, as generators look for that specific pattern, and ignore (or do not recognize) others. If somebody likes to create challenges beyond well described patterns, these might be worth a try.

[goldie5218]

hey come on guys ! its nice to have fun but what about a few 'straight' answers?? your examples of fancy terms/notions and names of obscure patterns may be very interesting to the experts amongst you, but quite frankly leaves me stone cold as i cant make head or tail of any of them - i watch this forum very carefully to see if i get any comeback and am dissapointed to read the vague and rambling theories that are probably very interesting to the researches amongst you, but toooo adavanced by far for my tiny little mind - now my question once again, just what is a turbot fish and should i be trying to identify it for solving the puzzles beyond the hard level of the simple suduko variety? i am managing quite well at this level but would like to try and improve my solving skills to the next level - (with some coaching hints if possible) do i graduate from "hard" knowing a little about swordfishes and xwings, then to "colours" ? and thereafter "forcing chains" then "turbot fishes" then...??????? cheers goldie