The New Sudoku Players' Forum

[urhegyi]

Code: Select all

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


[urhegyi]

So the point is due to the way I created the grids I can not know which of both grids is human solvable. Can anyone explain how to start solving for the 18 and 19 clue examples without first checking them with a solver to decide whichone to start solving first? I wonder how I should start solving them without a solver. Any tips?

[Hajime]

So the point is due to the way I created the grids I can not know which of both grids is human solvable. Can anyone explain how to start solving for the 18 and 19 clue examples without first checking them with a solver to decide whichone to start solving first? I wonder how I should start solving them without a solver. Any tips?

Independent of the jigsaw pieces 1r8c1 must be a 5...
And dependant on jigsaws 2r2c7 must be a 7 ...

[urhegyi]

So the point is due to the way I created the grids I can not know which of both grids is human solvable. Can anyone explain how to start solving for the 18 and 19 clue examples without first checking them with a solver to decide whichone to start solving first? I wonder how I should start solving them without a solver. Any tips?

Independent of the jigsaw pieces 1r8c1 must be a 5...
And dependant on jigsaws 2r2c7 must be a 7 ...

And because of in jigsaw 1 R8C1=5 the only other place for 5 in block1 = at R3C4!

[1to9only]

I wonder how I should start solving them without a solver. Any tips?

As with gattai (overlapped sudokus), I would part solve grid 1 making sure the overlapped region is updated from both grids, switch to grid 2 and repeat the process until twodoku is solved. This is how my rating program tends to work.

18-clues twodoku rating (5 passes of above solving 1, 2, 1, 2, ...):

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......5.....1..8..9......7681...........6..92..5..9...6.........7.836............ ED=2.9/1.2/1.2
............583.6.........7...6..8..96..2...........4523......9..1..4.....2...... ED=2.8/1.2/1.2


19-clues twodoku rating (4 passes):

Code: Select all

......5.....1..8..9......768......3..5..6...2..5..9...6.........7.836.....1...... ED=2.6/1.2/1.2
......9.....583.6.........7...6..8..9...2..7..9......523......9..1..4.....2...... ED=2.9/1.2/1.2


[1to9only]

I have semi-automated the twodoku generating - these from the same solution grids:

17-clues twodoku, Medium (3 passes!):

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.7....5.....1....83.6.......1..5.4...9..1.......86.......7.3...6.4............... ED=2.8/1.7/1.7
...............8.7...5.2.......34.......7..5...3.2..7.......1.97....5.....4....2. ED=2.9/1.5/1.5


16-clues twodoku, Easy (1 pass!):

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...4..5........7........98....65...2..........3...51..5.1.4.....2........5....... ED=2.0/1.2/1.2
.......3........4.....1.9.3..87...9..........6...21....72........6........4..8... ED=1.5/1.2/1.2


[Hajime]

Same puzzle, easy (naked/hidden singles only), with 15 resp 16 clues.
So each grid is not solvable on its own.

Code: Select all

#2//B4,JS/H16,JS
...2.35......9.........1..6...............3.22..6....86.83..............4........
111112222114122233444155223644555553644455333667777733668777999668788999688888999
....1..3......3.6.......4.....6.....96....5.....87...5.......1..7..........7....6
111222224111223244111333244553333344555669994566666994577668999557778988777788888

[1to9only]

You have to generate quite a few twodokus before you start finding the harder ones: below are same solution grids (but different from previous twodokus):

18-clues, Hard (7 passes):

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....1.3.8..4...6....93.8...82.........3.2.7....6.......61......3..1.............. ED=4.2/1.5/1.5
..............4..1......86.......3....4.5.1.........92...3.24....9...2..2.3.6.... ED=4.0/1.2/1.2


18-clues, Harder (8 passes):

Code: Select all

64...9.7.9..85......9..82...2.4..1....3..........9.......28.............7........ ED=4.2/1.2/1.2
........8.............29.......8..........1....6..1.9...83..4......47..5.7.5...14 ED=4.2/2.6/2.6


[urhegyi]

Same puzzle, easy (naked/hidden singles only), with 15 resp 16 clues.
So each grid is not solvable on its own.

Code: Select all

#2//B4,JS/H16,JS
...2.35......9.........1..6...............3.22..6....86.83..............4........
111112222114122233444155223644555553644455333667777733668777999668788999688888999
....1..3......3.6.......4.....6.....96....5.....87...5.......1..7..........7....6
111222224111223244111333244553333344555669994566666994577668999557778988777788888

Could you check the uniqueness of grid 1 by filling in the overlapping cells? I think it has multiple solutions.

[Hajime]

Indeed, a lot of attempts to generate a difficult jigsaw twodoku puzzle.

Code: Select all

#2//B4,JS/H16,JS
4.........6...2.......2.........8...7.4...9..1.8..3.....597.....4...6...2........
111112222114122233444155223644555553644455333667777733668777999668788999688888999
...17..9.................148................7...5.7.....52.........6..8......3.5.
111222224111223244111333244553333344555669994566666994577668999557778988777788888

To solve this puzzle with SiSeSuSo.exe, one X-chain and two XY-chains were needed. That is about SER 7, I think.

[urhegyi]

Indeed, a lot of attempts to generate a difficult jigsaw twodoku puzzle.

Code: Select all

#2//B4,JS/H16,JS
4.........6...2.......2.........8...7.4...9..1.8..3.....597.....4...6...2........
111112222114122233444155223644555553644455333667777733668777999668788999688888999
...17..9.................148................7...5.7.....52.........6..8......3.5.
111222224111223244111333244553333344555669994566666994577668999557778988777788888

To solve this puzzle with SiSeSuSo.exe, one X-chain and two XY-chains were needed. That is about SER 7, I think.

I think it has the same problem: found 3 different solutions.

[1to9only]

I've found one twodoku that requires chains, grid 1 solves first, then grid 2 needs chains to solve:

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...........4.........3....682....1....36.5.1.....9.5.4..1......3....7.....8...... ED=3.4/1.2/1.2
......6.....9....1......8..7.5.8.....9.2.31....6....925....2.........2........... ED=7.2/1.2/1.2


[Hajime]

Could you check the uniqueness of grid 1 by filling in the overlapping cells? I think it has multiple solutions.

I can find only 1 solution:

Code: Select all

#2//B4,JS/H16,JS
749283561362194857983541276816725934157468392235679418698312745574836129421957683
111112222114122233444155223644555553644455333667777733668777999668788999688888999
745216938129583764683195427517642893964328571396871245238457619871964352452739186
111222224111223244111333244553333344555669994566666994577668999557778988777788888

On its own grid 1 will surely have more solutions. But by interacting with grid 2 there is only 1, I think.
Can you post your different solutions?

[1to9only]

Could you check the uniqueness of grid 1 by filling in the overlapping cells? I think it has multiple solutions.

I can find only 1 solution:

This can be explained by the fact that JigsawExplainer uses the original SE solving techinques, and Hajime's SiSeSuSo.exe has implemented other solving techniques.

[urhegyi]

Could you check the uniqueness of grid 1 by filling in the overlapping cells? I think it has multiple solutions.

I can find only 1 solution:

Code: Select all

#2//B4,JS/H16,JS
749283561362194857983541276816725934157468392235679418698312745574836129421957683
111112222114122233444155223644555553644455333667777733668777999668788999688888999
745216938129583764683195427517642893964328571396871245238457619871964352452739186
111222224111223244111333244553333344555669994566666994577668999557778988777788888

On its own grid 1 will surely have more solutions. But by interacting with grid 2 there is only 1, I think.
Can you post your different solutions?

For R2C3 I can take 2 or 7 when taking R2C3 = 7 then I can take 1 or 5 for R5C2.
When taking R2C3 = 2 then I can take 1 or 5 for R5C2 too.

R2C3=7 R5C2=5 (sol1)
R2C3=2 R5C2=5 (sol2)
R2C3=7 R5C2=1 (sol3)
R2C3=2 R5C2=1 then I can take R2C6 4 or 8
R2C3=2 R5C2=1 R2C6=8 R2C7=4 R49C46 =UR 79 (2 options) (sol3 sol4)
R2C3=2 R5C2=1 R2C6=4 R2C7=8 (sol5)

In total 5 solutions
P.S. Your second grid is the same as mine.