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This is a place chosen to make available some ideas (on puzzles, patterns, etc)
that seemed unsuitable for posting in a Forum, but some people may find interesting.
For difficult puzzles (like the next one), possible solutions will not be shown (only hints).
For other puzzles, the solution wil be hidden so that a serious attempt can be made
without direct access to a solution.
(hopefully this will make the puzzles more interesting for newcomers).
I propose this interesting tough 9x9 Classic Sudoku puzzle.
It is solvable in three (krakenless) steps.
(found with Sudoku Architect)
,--------------------------------------------------------------------,
| 4789 4789 1 | 479 5 6 | 79 3 2 |
| 5679 579 3 | 279 8 27 | 4 56 1 |
| 45679 2 469 | 1 379 347 | 579 8 67 |
|----------------------+----------------------+----------------------|
| 13457 1457 48 | 4567 167 4578 | 2 9 345 |
| 34579 4579 2489 | 2457 27 24578 | 6 1 345 |
| 145 6 24 | 3 12 9 | 8 7 45 |
|----------------------+----------------------+----------------------|
| 2 19 5 | 679 3679 37 | 13 4 8 |
| 469 3 469 | 8 29 1 | 57 256 67 |
| 168 18 7 | 25 4 235 | 13 26 9 |
'--------------------------------------------------------------------'
Update (Dec 8, 2025)
There is a powerful move the reduces SE to 7.1. The idea (often used)
is to look for almost wings in the puzzle. There are at least two of
them, but it seems that only one is useful.
So, the task is to find such almost wing and try to see if the spoiler
leads to the same elimination of the wing.
I have a more challenging Slitherlink puzzle (compared to SL# 16).
(puzzle from Simon Tatham's Collection)
.-----------------------------------.
| . . . . . . . . . |
| 2 2 3 | 8
| . . . . . . . . . |
| 3 3 2 2 0 3 | 7
| . . . . . . . . . |
| 1 2 1 | 6
| . . . . . . . . . |
| 3 2 2 0 2 2 | 5
| . . . . . . . . . |
| 2 | 4
| . . . . . . . . . |
| 3 2 2 1 | 3
| . . . . . . . . . |
| 2 | 2
| . . . . . . . . . |
| 1 3 2 1 3 | 1
| . . . . . . . . . |
'-----------------------------------'
a b c d e f g h
Update (Dec4, 2025)
Basic moves
.-----------------------------------.
| . . . . . .___. . . |
| x 2 2 | 3 | | 8
| . . . . .___. .___. . |
| | 3 | 3 | 2 2 0 3 | | 7
| . . . . . . .___. x . |
| x 1 2 | x 1 | 6
| . . . . . . .___.___. |
| 3 2 2 0 x 2 x 2 | | 5
| . . . . . . .___. x . |
| 2 | | | | 4
| . . . . . . . . . |
| | 3 2 2 1 | 3
| .___. . . . . . . . |
| x 2 | 2
| . x . . . x . . . . . |
| x 1 | 3 2 x 1 3 | 1
| . x .___. . .___. . . . |
'-----------------------------------'
a b c d e f g h
Update (Dec 05, 2025)
Step 2: (2l)e7 is impossible because
creates a line at (2t)d8 without
place to go. So, (2b)e7 and a few
placements are available.
[recall notation: (2l)e7 means a line
in the left edge of the cell e7, that
has a 2 in it]
.-----------------------------------.
| . . . . . .___. . . |
| x 2 2 | 3 | | 8
| . . . . .___. .___. . |
| | 3 | 3 | 2 2 0 3 | | 7
| . . . .___.___. .___. . |
| x 1 2 | | 1 | 6
| . . . . .___. .___.___. |
| 3 2 2 0 2 2 | | 5
| . . . . . . .___. . |
| 2 | | | | 4
| . . . . . . . . . |
| | 3 2 2 1 | 3
| .___. . . . . . . . |
| 2 | 2
| . . . . x . . . . . |
| 1 | 3 2 x 1 3 | 1
| . .___. . .___. . . . |
'-----------------------------------'
a b c d e f g h
How to make progress from here ?
Update (Dec 7, 2025)
Step 3: Due to the line (2 t)e7, we must
have (2t)c8 ...
.-----------------------------------.
| . . .___. . .___. . . |
| x 2 2 | 3 | | 8
| . . . . .___. .___. . |
| | 3 | 3 | 2 2 0 3 | | 7
| . . . .___.___. .___. . |
| x 1 2 | | 1 | 6
| . . . . .___. .___.___. |
| 3 2 2 0 2 2 | | 5
| . . . . . . .___. . |
| 2 | | | | 4
| . . . . . . . . . |
| | 3 2 2 1 | 3
| .___. . . . . . . . |
| 2 | 2
| . . . . x . . . . . |
| 1 | 3 2 x 1 3 | 1
| . .___. . .___. . . . |
'-----------------------------------'
a b c d e f g h
and that line cannot go down: (2l)c8, (3b)b7
lead to impossibility at (2)c6, so ( t)b8 and
many placements follow:
.-----------------------------------.
| .___.___.___. . .___. . . |
| | 2 | 2 | 3 | | 8
| . .___. .___.___. .___. . |
| | 3 | 3 | 2 2 0 3 | | 7
| .___. .___.___.___. .___. . |
| 1 2 | | 1 | 6
| .___.___.___. .___. .___.___. |
| | 3 2 2 0 2 2 | | 5
| .___. . . . . .___. . |
| 2 | | | | 4
| .___. . . . . . . . |
| | 3 2 2 1 | 3
| .___. . . . . . . . |
| 2 | 2
| . . . . x . . . . . |
| 1 | 3 2 x 1 3 | 1
| . .___. . .___. . . . |
'-----------------------------------'
a b c d e f g h
Update (Dec 8, 2025)
Step 4: ( r)a2 is not possible because it
quickly leads to a loop.So (3t)b1
and many placemens follow.
.-----------------------------------.
| .___.___.___. . .___. . . |
| | 2 | 2 | 3 | | 8
| . .___. .___.___. .___. . |
| | 3 | 3 | 2 2 0 3 | | 7
| .___. .___.___.___. .___. . |
| 1 2 | | 1 | 6
| .___.___.___. .___. .___.___. |
| | 3 2 2 0 2 2 | | 5
| .___. . . . . .___. . |
| 2 | | | | 4
| .___. . . . . . . . |
| | 3 2 2 1 | 3
| .___.___. . . . . . . |
| | | 2 | 2
| . .___.___. x .___. . . . |
| 1 | 3 2 x 1 3 | | 1
| . .___.___.___.___. . . . |
'-----------------------------------'
a b c d e f g h
Now we need to resolve the center and that (2)g2 isolated
and this can be done in two more moves.
Created: February 12, 2024
Contact: sudo.jco.br@gmail.com