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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 and hard Slitherlink puzzle.
(puzzle from Simon Tatham's Collection)
.-----------------------------------.
| . . . . . . . . . |
| 2 2 3 | 8
| . . . . . . . . . |
| 2 2 2 2 | 7
| . . . . . . . . . |
| 2 2 3 3 3 | 6
| . . . . . . . . . |
| 3 | 5
| . . . . . . . . . |
| 3 2 2 2 0 1 | 4
| . . . . . . . . . |
| 1 3 1 | 3
| . . . . . . . . . |
| 2 2 | 2
| . . . . . . . . . |
| 3 2 1 3 | 1
| . . . . . . . . . |
'-----------------------------------'
a b c d e f g h
Update (Nov 24, 2025)
We have many basic moves at the start.
Most of them are in the following grid
.-----------------------------------.
| . .___. . . .___.___.___. |
| 2 2 3 | | 8
| . . . . . . .___.___. |
| | 2 2 2 2 | 7
| . . . . . . . .___. |
| 2 2 3 3 3 | | 6
| . . . . . . . . . |
| |3 | 5
| . . . . . . .___. . |
| 3 2 2 2 0 1 | 4
| . . . . . .___. . . |
| 1 | 3 1 | 3
| . . . . . . . . . |
| 2 2 | 2
| . . . . . . . . . |
| | 3 2 1 3 | | 1
| .___. . . . . . .___. |
'-----------------------------------'
a b c d e f g h
Update (Nov 27, 2025)
. looking at (3)g3 to make progress at h1
. (2)f7 interacts with (3)e6
.-----------------------------------.
| . .___. . . .___.___.___. |
| 2 2 3 | | 8
| . . . . . . .___.___. |
| | 2 2 2 2 | 7
| . . . . . . . .___. |
| 2 2 3 | 3 3 | | 6
| . . . . x .___. . . . |
| x |3 | 5
| . . . . x . x . .___. . |
| 3 2 2 | 2 x 0 1 | 4
| . . . .___. x .___. . . |
| 1 | | 3 | 1 | 3
| . . . . . . .___. x . |
| 2 2 x | 2
| . . . . . . .___.___. |
| | 3 2 1 3 | | 1
| .___. . . . .___.___.___. |
'-----------------------------------'
a b c d e f g h
How to continue ?
Update (Nov 29, 2025)
Looking at (2)a2, the line at (3l)a1 must
enter (1)b3, so (x) at the top and right of
that cell. That makes impossible having a
line at (2)b4, so (2lb4), (2t)b4, and (2t)c4,
etc
.-----------------------------------.
| . .___. . . .___.___.___. |
| 2 2 3 | | 8
| . . . . . . .___.___. |
| | 2 2 2 2 | 7
| . . . . . . . .___. |
| 2 2 3 | 3 3 | | 6
| . . . . .___. . . . |
| | |3 | 5
| . .___.___. . . .___. . |
| | 3 | 2 2 | 2 0 1 | 4
| .___. x . .___. .___. . . |
| 1 x | | 3 | 1 | 3
| . .___. . . . .___. x . |
| 2 2 x | 2
| . . . . . . .___.___. |
| | 3 2 1 3 | | 1
| .___. . . . .___.___.___. |
'-----------------------------------'
a b c d e f g h
How far can we go before getting stuck ?
It turns out a deduction is needed already!
.-----------------------------------.
| . .___. . . .___.___.___. |
| 2 2 3 | | 8
| . . . . . . .___.___. |
| | 2 2 2 2 | 7
| . . . . . . . .___. |
| 2 2 3 | 3 3 | | 6
| . . . . .___. . . . |
| | |3 | 5
| . .___.___. . . .___. . |
| | 3 | 2 2 | 2 0 1 | 4
| .___. x . .___. .___. . . |
| 1 x | | 3 | 1 | 3
| . .___. . . . .___. x . |
| 2 2 x | 2
| . . . . . . .___.___. |
| | 3 2 1 3 | | 1
| .___. . . . .___.___.___. |
'-----------------------------------'
a b c d e f g h
One possibility is to analyze where ( l)a5 should go.
( l)a6 is not possible because it quickly leads into
an impossible loop at cells b6,b7,c6.
So, (2b)a6 is forced and after many placements, we get
.-----------------------------------.
| .___.___.___. . .___.___.___. |
| | 2 | 2 | 3 | | 8
| . . . .___. . .___.___. |
| | 2 2 | | 2 | 2 | 7
| .___.___.___. . . . .___. |
| 2 2 3 | | 3 | 3 | | 6
| .___.___.___. .___. . . . |
| | |3 | 5
| . .___.___. . . .___. . |
| | 3 | 2 2 | 2 0 1 | 4
| .___. . .___. .___. . . |
| 1 | | 3 | 1 | 3
| . .___. . . . .___. . |
| 2 2 | 2
| . . . . . . .___.___. |
| | 3 2 1 3 | | 1
| .___. . . . .___.___.___. |
'-----------------------------------'
a b c d e f g h
What can we do next ?
Update (Nov 02, 2025)
(3r)g5 is not possible, because
it forces ( r)h5 to get an even number
of lines at row 5 and that leads to
trouble of a line at ( r)h4 that has
no place to go downwards. So, (3t)g5
is the only way, leading to
.-----------------------------------.
| .___.___.___. . .___.___.___. |
| | 2 | 2 | 3 | | 8
| . . . .___. . .___.___. |
| | 2 2 | | 2 | 2 | 7
| .___.___.___. . . .___.___. |
| 2 2 3 | | 3 | 3 | | 6
| .___.___.___. .___. .___.___. |
| | |3 | 5
| . .___.___. . . .___. . |
| | 3 | 2 2 | 2 0 1 | | 4
| .___. . .___. .___. . . |
| 1 | | | 3 | 1 | 3
| . .___. . . . .___. . |
| 2 2 | 2
| . . . . . .___.___.___. |
| | 3 2 1 3 | | 1
| .___. . . .___.___.___.___. |
'-----------------------------------'
a b c d e f g h
here we are very close to done.
Update (Nov 3, 2022)
Clearly the line ( r)e3 must go down to avoid a loop.
Also, (3t)a1 is not possible (why?) and the alternative
solves the puzzle with singles afterwards.
.-----------------------------------.
| .___.___.___. . .___.___.___. |
| | 2 | 2 | 3 | | 8
| . . . .___. . .___.___. |
| | 2 2 | | 2 | 2 | 7
| .___.___.___. . . .___.___. |
| 2 2 3 | | 3 | 3 | | 6
| .___.___.___. .___. .___.___. |
| | |3 | 5
| . .___.___. . . .___. . |
| | 3 | 2 2 | 2 0 1 | | 4
| .___. . .___. .___. . . |
| 1 | | | 3 | 1 | 3
| .___.___.___.___. . .___. . |
| | 2 2 | | 2
| . .___.___.___. .___.___.___. |
| | 3 | 2 1 | 3 | | 1
| .___. . . .___.___.___.___. |
'-----------------------------------'
a b c d e f g h
Created: February 12, 2024
Contact: sudo.jco.br@gmail.com