The New Sudoku Players' Forum

[AnotherLife]

Hi everyone,
I was offered this puzzle for solving on a website. It looks like a silly game where a player earns some points for a solution no matter how difficult the task is. Earlier they gave me sudokus solvable with only the so called 'basic steps', but here it is, the sudoku rated SKFR 7.3. Maybe a player is supposed to use their hints but I never use them as I have to give up in this case, figuratively speaking. Anyway, I do not understand what is inside their heads.

.4..932.........6.1..4....5.....6.......38.9.....4.8...7.5..9.642.....5.5.......7

*-----------*
|.4.|.93|2..|
|...|...|.6.|
|1..|4..|..5|
|---+---+---|
|...|..6|...|
|...|.38|.9.|
|...|.4.|8..|
|---+---+---|
|.7.|5..|9.6|
|42.|...|.5.|
|5..|...|..7|
*-----------*
Please, do not use computer methods, automated pencil marks and highlights.

[eleven]

Pretty hard puzzle, which I did not solve manually.
But there is a move, which can be spotted and helps you.

Code: Select all

  +-----------+-----------+-----------+
  |  .  4  5  |  .  9  3  |  2  8  1  |
  |  .  .  .  |  .  5  .  |  4  6  9  |
  |  1  .  .  |  4 *68 2  |  7  3  5  |
  +-----------+-----------+-----------+
  |  .  .  .  |  .  . *6  |  5  .  .  |
  |  .  5  .  |  .  3 *8  |  6  9  .  |
  |  .  .  .  |  .  4  5  |  8  .  .  |
  +-----------+-----------+-----------+
  |  .  7  .  |  5  .  .  |  9  .  6  |
  |  4  2  .  |  3* .  .  |  .  5  8  |
  |  5  .  .  |  3* .  .  |  .  .  7  |
  +-----------+-----------+-----------+

Note the candidates 68 in r3c5 and 3 restricted to r89c4.
If r3c5=6, it has to go to r89c4 to give a pair 36 there.
If it is 8, you get a pair 38.
So r89c4 can only have the digits 368 (not 1279), and 2 is locked to r789c5, leaving a pair 17 in r4c58.

It is still not easy, but now can be solved with locked candidates, pairs, a (grouped) kite for 8 (r9c3<>8), and a w-wing 76 (strong link for 7 in c6), removing 6 from r3c5 and r89c4.

[AnotherLife]

Hi Eleven,
I get your solution, thank you. I think I should learn to be able to solve sudokus with such simple and useful considerations.
Actually, I managed to find an efficient solution to the puzzle but it took some time and effort. I used the old ALS-based technique that I mastered thanks to JCO who has unfortunately become my enemy. So here it is.

Code: Select all

.------------------------.--------------------.-------------.
| g67      4      5      | h67     9      3   | 2   8   1   |
|  2378   e38     2378   | b178    5     a1-7 | 4   6   9   |
|  1       689    689    |  4      68     2   | 7   3   5   |
:------------------------+--------------------+-------------:
|  23789  e138    123478 |  1279   127    6   | 5   17  234 |
|  27      5     d1247   | c127    3      8   | 6   9   24  |
| f23679  e136    12367  |  1279   4      5   | 8   17  23  |
:------------------------+--------------------+-------------:
|  38      7      138    |  5      128    14  | 9   24  6   |
|  4       2      169    |  136-7  167   *179 | 13  5   8   |
|  5       1689   1689   |  12368  1268   149 | 13  24  7   |
'------------------------'--------------------'-------------'

(1)r2c6=r2c4-r5c4=r5c3-(1=6)r246c2-r6c1=r1c1-(6=7)r1c4 => -7 r2c6
(Sorry if I have forgotten how to write these formulae.)
From now on the puzzle can be solved by some basic steps and an empty rectangle (or skyscraper).
Maybe this method is pretty hard but I apply what I managed to learn on this forum and from HoDoKu thanks to Bernhard Hobiger.