JCO Website (Puzzles for the manual solver)

Welcome!

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).

Puzzles

Puzzle SX#8 (overall #78) (6x6 Sudoku-X (SE = 7.2); proposed Oct 11, 2025)

I propose the following Sudoku-X puzzle.

I have solved it (manually) in 3 steps with simple chains.

(generated and displayed with Sudoku6Explainer)

Sudoku-X

Hint (For now, just grid after basics)

 After performing basic moves:
+-------------------+-------------------+
| 3     246   246   | 5     246   1     |
| 145   1245  12456 | 46    3     246   |
+-------------------+-------------------+
| 145   16    456   | 2     45    3     |
| 2     3     45    | 146   1456  456   |
+-------------------+-------------------+
| 145   45    12    | 3     2456  2456  |
| 6     245   3     | 14    1245  245   |
+-------------------+-------------------+
                                         Sudoku-X

Puzzle 6x6CS#4 (overall #79) (6x6 Classic Sudoku (SE = 7.2); proposed Oct 11, 2025)

I have solved (manually) the following interesting puzzle in 4 steps.

Probably there is a shorter way to be found after further analysis.

(generated and displayed with Sudoku6Explainer)

Classic Sudoku 6x6

Hint (For now, just the grid after basics)

 After performing basic moves:
+----------------+----------------+
| 26   4    5    | 1    3    26   |
| 3    126  12   | 24   5    246  |
+----------------+----------------+
| 1    235  234  | 6    24   245  |
| 245  25   6    | 245  1    3    |
+----------------+----------------+
| 2456 2356 234  | 245  24   1    |
| 245  125  124  | 3    6    245  |
+----------------+----------------+
                                   6x6 CS

Puzzle CS#35 (#80 overall) (9x9 Classic Sudoku; SE = 7.2; proposed Oct 12, 2025)

I have an interesing tough 9x9 Classic Sudoku puzzle!

I could not stop battling with it until it was solved (manually) in 4 steps.

There must be a simpler way (further analysis needed).

Classic Sudoku

(found with Sudoku Architect)

Hint (For now, just the grid after basics)

After performing the basics moves:
,--------------------------------------------------------,
| 7    145    145   | 56   9   2    | 3468    3468   38  |
| 3    9      45    | 567  58  678  | 2       46     1   |
| 6    2      8     | 1    4   3    | 79      5      79  |
|-------------------+---------------+--------------------|
| 15   13456  13456 | 9    7   18   | 3458    348    2   |
| 9    8      357   | 2    6   4    | 357     1      357 |
| 2    14     147   | 3    18  5    | 4789    4789   6   |
|-------------------+---------------+--------------------|
| 158  1356   1356  | 567  2   1679 | 136789  36789  4   |
| 4    7      2     | 8    3   169  | 1569    69     59  |
| 158  1356   9     | 4    15  167  | 13678   2      378 |
'--------------------------------------------------------'

Try also the recently proposed 9x9 Sudoku puzzle (at NSPF) here

Past proposed 9x9 CLASSIC SUDOKU PUZZLES (34) are HERE
Past proposed SLITHERLINK PUZZLES (14) are HERE
Past proposed 9x9 JIGSAW SUDOKU PUZZLES (6) are HERE
Past proposed 6x6 SUDOKU-X PUZZLES (7) are HERE
Past proposed LATIN SQUARES PUZZLES (6) are HERE
Past proposed HIDOKU PUZZLES (5) are HERE
Past proposed 6x6 CLASSIC SUDOKU PUZZLES (4) are HERE
Past proposed HASHI PUZZLES (1) are HERE

Problems

Slitherlink and Jigsaw Sudoku Layouts

Problem #1

Slitherlink

In the game called Slitherlink, can you show all the details

proving that the following configuration is impossible ?

Impossible pattern 222x

Hidden solution

Part 1

(My solution has a trivial initial observation, an easy Case 1 and Case 2 divided in two sub-cases)

We analyze the possible outcomes from this configuration but can already discard

all configurations in which the lower "2"-cell has vertical lines, or horizontal lines,

in both edges.

Also, this configuration

.-------------------
| .   .   .   .   . 
|           2       
| .   .   .   .   . 
|       2           
| .___.   .   .   . 
| | 2               
|A.   .   .   .   . 
| x                 
| .   .   .   .   .

and this

.-------------------
| .   .   .   .   . 
|           2       
| .   .   .   .   . 
|       2           
| .   .   .   .   . 
|   2 |             
|A.___.   .   .   . 
| x                 
| .   .   .   .   .

are clearly impossible,

(dead end at corner A).

Part 2

Case 1:

.-------------------
| .   .   .   .   . 
|           2       
| .   .   .   .   . 
|       2           
| .___.   .   .   . 
|   2 |             
| .   .   .   .   . 
| x                 
| .   .   .   .   .

Now the following is forced

.-------------------
| .   .___.___.   . 
|         x 2 |     
| .   .___. x .   . 
| |   x 2 |         
| .___. x .   .   . 
|   2 |             
| .   .   .   .   . 
| x                 
| .   .   .   .   .

and this leads to an impossibility in the cell at the corner, reached by three lines.

Part 3

Case 2:

.-------------------
| .   .   .   .   . 
|           2       
| .   .   .   .   . 
|       2           
| .   .   .   .   . 
| | 2               
| .___.   .   .   . 
| x                 
| .   .   .   .   .

The following is a forced move

.-------------------
| .   .   .   .   . 
|           2       
| .   .B  .   .   . 
| |     2           
| . x .A  .   .   . 
| | 2 x             
| .___.   .   .   . 
| x                 
| .   .   .   .   .

Part 3.1

Case 2.1: If a vertical line exists at AB, it forces

.-------------------
| .   .   .   .   . 
|     |     2       
| .C  .   .   .   . 
| |   | 2           
| . x .___.D  .   . 
| | 2 x             
| .___.   .   .   . 
| x                 
| .   .   .   .   .

and any continuation for the line meeting corner C will create a loop (impossible).

Part 3.2

Case 2.2: the other possibility is to have the edge AB blocked, and then the bottom edge AD

of the "2"-cell in the middle needs to be blocked too, forcing the following configuration to be reached.

.-------------------
| .   .___.___.   . 
|         x 2 |     
| .   .___. x .   . 
| |   x 2 |         
| . x . x .   .   . 
| | 2 x             
| .___.   .   .   . 
| x                 
| .   .   .   .   .

Now, we have an impossible situation in the cell at the corner, reached by three lines. □

(Using symmetry, the proven result establishes a well-known slitherlink pattern)