The New Sudoku Players' Forum

[mayres]

Can you please give help me out with Sudoku for Dummies puzzle #201?
The puzzle starts like this

Code: Select all

 
 *-----------*
 |...|3..|6..|
 |...|..7|8..|
 |9.7|6..|1.2|
 |---+---+---|
 |87.|.4.|..9|
 |..3|...|7..|
 |1..|.3.|.86|
 |---+---+---|
 |4.2|..6|5.7|
 |..1|2..|...|
 |..9|..3|...|
 *-----------*


I have managed to get to the following place and am now stuck wondering what the next move is to illiminate something or determine the number for a cell????

Code: Select all

 *--------------------------------------------------------------------*
 | 25     124    8      | 3      1259   1459   | 6      7      45     |
 | 36     1246   45     | 145    125    7      | 8      9      345    |
 | 9      34     7      | 6      58     458    | 1      345    2      |
 |----------------------+----------------------+----------------------|
 | 8      7      6      | 15     4      125    | 3      125    9      |
 | 25     249    3      | 1589   6      12589  | 7      1245   145    |
 | 1      249    45     | 7      3      259    | 24     8      6      |
 |----------------------+----------------------+----------------------|
 | 4      38     2      | 189    189    6      | 5      13     7      |
 | 367    568    1      | 2      578    458    | 9      46     348    |
 | 67     568    9      | 1458   1578   3      | 24     1246   148    |
 *--------------------------------------------------------------------*


THANKS! mike

[udosuk]

For this type of puzzles I definitely recommend you to acquire a solver program such as Angus Johnson's Simple Sudoku (available from this link). It doesn't need extremely advanced moves to solve, but you do have to apply quite a lot of higher-level techniques such as swordfish, turbot fish (colors), xy-wing etc. If you use Simple Sudoku you'd get to see all these moves explained to you visually and clearly.

There is perhaps a one-move-kill-it-all ALS-xz or forcing chain somewhere in there, but I suppose you'd learn more if you take the trouble to learn the Simple Sudoku technique set (what we call SSTS) first.

As for the next few moves for this puzzle, I'll post below using "invisible ink" :

Swordfish on 4s (r269c347) => 4 eliminated from else of r269
Turbot fish on 5s (strong links r15c1+r6c36, r1c6<>5)
XY-wing {345} (r2c3=4|5 => either r2c9=3|5 or r3c2=3|4 must be 3 => r2c1,r3c8<>3)

[mayres]

Do you know of an exceptionally good illustration/treatise on swordfish technique? I've querried a few on the internet, but I'm having a problem visualizing which cells to pick when I see a puzzle. On illustrations that people use I wonder why they picked those cells versus other options that seem to be just as valid (but I'm sure are not - I'm just missing an important part of the concept). Thanks for the suggestions and I am definately making the effort to process the three concepts you have listed. I'd like to not move on until I have these down pat.
Thanks again - mike

[MCC]

mayres, you might like to look at this link.
http://www.sudopedia.org/wiki/Swordfish


MCC

[re'born]

For a different approach, try arcilla's thread.

[Steve48]

Do you know of an exceptionally good illustration/treatise on swordfish technique? I've querried a few on the internet, but I'm having a problem visualizing which cells to pick when I see a puzzle.

Based on the point that you reached in your initial posting, I would speculate that you do understand x-wings. You seem to have applied one on 3's to get to where you did (though you could have used coloring). The swordfish concept is much the same as the x-wing concept, but extended to 3 columns (or rows) of 3, instead of 2 columns (rows) of 2. What complicates things, and makes the swordfish even harder to spot, is that a column of 3 might actually only have 2 candidate cells. Hmmm. Not sure that makes it any clearer, but if you understand x-wing, then swordfish are certainly within your grasp.

[udosuk]

For a different approach, try arcilla's thread.

Here are the pencilmark grid and the converted column-digit and row-digit tables (# used to denote the digits):

Code: Select all

 25    124   8     | 3     1259  1459  | 6     7     45
 36    1246  45    | 145   125   7     | 8     9     345
 9     34    7     | 6     58    458   | 1     345   2
-------------------+-------------------+-----------------
 8     7     6     | 15    4     125   | 3     125   9
 25    249   3     | 1589  6     12589 | 7     1245  145
 1     249   45    | 7     3     259   | 24    8     6
-------------------+-------------------+-----------------
 4     38    2     | 189   189   6     | 5     13    7
 367   568   1     | 2     578   458   | 9     46    348
 67    568   9     | 1458  1578  3     | 24    1246  148

#1 | 6      12     8      | 24579  1279   145    | 3      4579   59
#2 | 15     1256   7      | 8      12     456    | 69     459    3
#3 | 28     37     5      | 1      6      9      | 4      37     28
#4 | 7      12356  26     | 29     4      138    | 69     3589   12589
#5 | 15     89     26     | 2459   12389  134568 | 7      345    125
#6 | 289    289    4      | 3      5      7      | 1      89     6
#7 | 89     4      3      | 6      89     2      | 5      1      7
#8 | 4      789    1      | 579    3789   358    | 2      6      89
#9 | 3      56     9      | 57     17     156    | 8      2      4

 #1    #2    #3    #4    #5    #6    #7    #8    #9
-----------------------------------------------------
 256   125   4     269   1569  7     8     3     56
 245   25    19    2349  3459  12    6     7     8
 7     9     28    268   568   4     3     56    1
-----------------------------------------------------
 468   68    7     5     468   3     2     1     9
 4689  1268  3     289   14689 5     7     46    246
 1     267   5     237   36    9     4     8     26
-----------------------------------------------------
 458   3     28    1     7     6     9     245   45
 3     4     19    689   256   128   15    2569  7
 4589  78    6     4789  245   128   15    2459  3

As you can see from the column-digit table, there is a naked triple {269} for digit 4 on d4c347, which means a swordfish of 4 on r269c347 and all other 4s on those 3 rows must be eliminated.

On the row-digit table you'll in turn find a hidden triple {347} on r269d4 (or a naked quad {2689} on r1358d4 which represents the dual jellyfish of 4 on r1358c2689).

[ronk]

re'born and udosuk, as of today mayres has only 16 posts here and was having some difficulty with the swordfish technique.

I hope introducing him to the very advanced rn-space and cn-space, as Denis Bernier calls it, doesn't scare him away from sudoku forever.

[Steve48]

If the advanced technique tends to scare him away, hopefully Udosuk's suggestion of acquiring Simple Sudoku will push him a long way in the right direction.

The puzzle that he brought is the scariest thing in this thread. If that comes from something called Sudoku for Dummies, I'd hate to see a puzzle that they figure is for smart folk.

[Pat]

The puzzle that he brought is the scariest thing in this thread.

If that comes from something called Sudoku for Dummies,
I'd hate to see a puzzle that they figure is for smart folk.

the series of books "for Dummies" -- despite the name -- is not intended for dummies

they start from the beginning -- and may advance quite far

some tough puzzles from Sudoku for Dummies have been mentioned