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, 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)
(Guidelines for using this site here)
(useful to look up for the meaning of some unfamiliar concept)
I propose this newly created Hidoku puzzle (for a manual solution !)
.---------------------------.
7 | 16 __ __ __ __ __ 49|
6 | __ 19 __ __ __ __ __|
5 | __ 27 __ __ __ __ __|
4 | __ 24 __ __ __ __ 10|
3 | 29 __ __ __ __ __ __|
2 | __ __ __ 34 39 __ 42|
1 | __ __ 35 __ __ __ 01|
'---------------------------'
a b c d e f g
I propose the following tough Classic Sudoku puzzle.
(found with Sudoku Architect)
After basics
,----------------------------------------------------------------,
9 | 2 36 589 | 468 45689 456 | 1 368 7 |
8 | 56 1 578 | 2 5678 3 | 689 4 69 |
7 | 369 367 4 | 1678 16789 16 | 5 368 2 |
|---------------------+--------------------+---------------------|
6 | 156 4 57 | 3 168 9 | 678 2 56 |
5 | 13569 367 2579 | 1468 12468 1246 | 46789 678 3569 |
4 | 369 8 29 | 5 246 7 | 469 1 369 |
|---------------------+--------------------+---------------------|
3 | 8 59 6 | 17 1257 125 | 3 79 4 |
2 | 4 2 3 | 9 67 8 | 67 5 1 |
1 | 7 59 1 | 46 3 456 | 2 69 8 |
'----------------------------------------------------------------'
a b c d e f g h i
Update 1 (Aug 27, 2026)
We have fishes on 6 and 7, but a much stronger move is available on
digits 7, 8.
This puzzle is solvable in one step with a powerful complex move.
The weakness of this puzzle is the box h2.
A simple way in two steps uses the patterns of digits 7, 8 to create
an elimination that gives one placement, and basics (1 LC, 1 NP).
After that a simple wing solves the puzzle.
However, by combining both ideas, one can solve this puzzle in one step.
Update 2 (Aug 28, 2026)
,----------------------------------------------------------------,
9 | 2 36 589 | 468 45689 456 | 1 368 7 |
8 | 56 1 578 | 2 5678 3 | 689 4 69 |
7 | 369 367 4 | 1678 16789 16 | 5 368 2 |
|---------------------+--------------------+---------------------|
6 | 156 4 57 | 3 168 9 | 678 2 56 |
5 | 13569 367 2579 | 1468 12468 1246 | 46789 67-8 3569 |
4 | 369 8 29 | 5 246 7 | 469 1 369 |
|---------------------+--------------------+---------------------|
3 | 8 59 6 | 17 1257 125 | 3 79 4 |
2 | 4 2 3 | 9 67 8 | 67 5 1 |
1 | 7 59 1 | 46 3 456 | 2 69 8 |
'----------------------------------------------------------------'
a b c d e f g h i
In two steps, for move 1, we remove (8)h5. Without (8)d7, there is
a Kite that removes that digit. However, that spoiler being true
also removes the same digit. One placement and basics leads to
,-------------------------------------------------------,
9 | 2 36 89 | 468 45689 456 | 1 38 7 |
8 | 5 1 78 | 2 78 3 | 69 4 69 |
7 | 369 367 4 | 1678 16789 16 | 5 38 2 |
|-----------------+-------------------+-----------------|
6 | 16 4 57 | 3 168 9 | 678 2 56 |
5 | 1369 367 2579 | 1468 12468 1246 | 46789 67 3569 |
4 | 369 8 29 | 5 246 7 | 469 1 369 |
|-----------------+-------------------+-----------------|
3 | 8 59 6 | 17 1257 125 | 3 79 4 |
2 | 4 2 3 | 9 67 8 | 67 5 1 |
1 | 7 59 1 | 46 3 456 | 2 69 8 |
'-------------------------------------------------------'
a b c d e f g h i
Now the puzzle is solved easily with a wing.
How to combine both ideas to solve the puzzle in a single step ?
Update 3 (Aug 30, 2026)
,----------------------------------------------------------------,
9 | 2 36 589 | 468 45689 456 | 1 368 7 |
8 | 56 1 578 | 2 5678 3 | 689 4 69 |
7 | 369 367 4 | 1678 16789 16 | 5 368 2 |
|---------------------+--------------------+---------------------|
6 | 156 4 *57 | 3 168 9 | 68-7 2 *56 |
5 | 13569 36-7 259-7 | 1468 12468 1246 | 46789 *67(8) 3569 |
4 | 369 8 29 | 5 246 7 | 469 1 369 |
|---------------------+--------------------+---------------------|
3 | 8 59 6 | 17 1257 125 | 3 79 4 |
2 | 4 2 3 | 9 67 8 | 67 5 1 |
1 | 7 59 1 | 46 3 456 | 2 69 8 |
'----------------------------------------------------------------'
a b c d e f g h i
There is a one-step solution removing (7)b5, c5, g6 with the following
logic: either the Y-wing (567)c6,i6,h5 is true, or (8)h5 is true.
However, (8)h5 true implies that (8)d7 must be true, and we already
noticed (in the solution in two-steps) that (8)d7 true implies (7)h5
being true.
So, either we have that Y-wing being true or (7)h5 is true. /////
Created: February 12, 2024
Contact: sudo.jco.br@gmail.com