The New Sudoku Players' Forum

[woodpecker]

got so far, then completely stuck. found the solution elsewhere, but cannot understand how to get to it. can someone please explain how to progress from this point?

4-7,---,2-1
--8,7-1,--4
31-,-4-,8-7

18-,67-,-4-,
--3,418,7--
74-,-95,1--

87-,-64,-19
-34,1-9,67-
961,--7,4-2

[wintder]

Code: Select all

.---------------.---------------.---------------.
| 4    59   7   | 3589 358  36  | 2    3569 1   |
| 256  259  8   | 7    235  1   | 359  3569 4   |
| 3    1    2569| 259  4    26  | 8    569  7   |
:---------------+---------------+---------------:
| 1    8   *259 | 6    7   *23  | 59   4    35  |
| 256  259  3   | 4    1    8   | 7    259  56  |
| 7    4    26  | 3-2  9    5   | 1    28   368 |
:---------------+---------------+---------------:
| 8    7   *25  |*235  6    4   | 35   1    9   |
| 25   3    4   | 1    258  9   | 6    7    58  |
| 9    6    1   | 358  358  7   | 4    358  2   |
'---------------'---------------'---------------'

You have here a horizontal skyscraper on the digit 2.
r4c3 and r7c3 cannot BOTH be 2. As there are strong links horizontally at least one of the other 2s, marked with "*", must be a 2. Whether it is one or both of them any cell that can "see" both 2s cannot be 2, thus you can remove the candidate 2 in r6c4.

[daj95376]

If you include row 3 in wintder's pattern for <2>, then you get a Swordfish that also eliminates the <2> in [r6c3]. Now, this certainly isn't any better than wintder's solution, but it's more likely to be what was intended from the puzzle generator perspective.

[re'born]

Another related solution is to note the empty rectangle in box 5 on 2, that along with the help of r7c34 eliminates 2 from r4c3, solving the puzzle.

Code: Select all

 *-----------------------------------------------------------*
 | 4     59    7     | 3589  358   36    | 2     3569  1     |
 | 256   259   8     | 7     235   1     | 359   3569  4     |
 | 3     1     2569  | 259   4     26    | 8     569   7     |
 |-------------------+-------------------+-------------------|
 | 1     8     259-  | 6*    7*    23*   | 59    4     35    |
 | 256   259   3     | 4*    1     8     | 7     259   56    |
 | 7     4     26    | 23*   9     5     | 1     28    368   |
 |-------------------+-------------------+-------------------|
 | 8     7     25&   | 235&  6     4     | 35    1     9     |
 | 25    3     4     | 1     258   9     | 6     7     58    |
 | 9     6     1     | 358   358   7     | 4     358   2     |
 *-----------------------------------------------------------*


[ravel]

Code: Select all

 *-----------------------------------------------------------*
 | 4     59    7     | 3589  358   36    | 2     3569  1     |
 | 256   259   8     | 7     235   1     | 359   3569  4     |
 | 3     1     25-69 | 259   4    *26    | 8     569   7     |
 |-------------------+-------------------+-------------------|
 | 1     8     259   | 6     7    #23    | 59    4     35    |
 | 256   259   3     | 4     1     8     | 7     259   56    |
 | 7     4    *26    |#23    9     5     | 1     28    368   |
 |-------------------+-------------------+-------------------|
 | 8     7     25    | 235   6     4     | 35    1     9     |
 | 25    3     4     | 1     258   9     | 6     7     58    |
 | 9     6     1     | 358   358   7     | 4     358   2     |
 *-----------------------------------------------------------*


No great help in this case is the semi-remote naked pair (W Wing) 26 with the strong link for 2 in box 5 (but once you have started to look for that, you will spot it):
If r4c6=2 then r3c6=6, if r6c4=2 then r6c3=6.
So r3c3 cannot be 6.

[Pat]

If you include row 3 in wintder's pattern for <2>,
then you get a Swordfish that also eliminates the <2> in [r6c3].

Now, this certainly isn't any better than wintder's solution,
but it's more likely to be what was intended from the puzzle generator perspective.

personally, i have a great preference for (un-finned) fish,
therefore i would certainly prefer daj95376's (un-finned) Swordfish

however, i am probably in a minority on this --
i suspect most would prefer the "finned fish" of order 2

Since I'm not familiar with all of the fish,
how should I select from the few that I do know?

The list of types of fish in the first post is also a difficulty ranking

choose the one with lowest ranking 1st (easiest)

the list has the basic un-finned earlier than any finned,
thus i could read tarek's comment as supporting my preference for the Swordfish in the above puzzle.

~ Pat

[woodpecker]

ta for all your replies. i had managed to fathom out how to eliminate the 2 in row 6 col 3 by description of a swordfish found on this site, not long after i asked the q.