Strategies for Number Puzzles of all kinds
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Wednesday 19-Sep-2018

... by: Paolo Calaresu

Basics J5=7;J7=8 and G1≠5.
After basics with only basics strategies
If A5=1=> B7≠1;B9≠4;C1≠23;C2≠3=>solution.

Tuesday 18-Sep-2018

... by: ghfick

Thanks very much, Cenoman!

Just slightly more than a 'simple' AIC.
I need to study Steve K's blog as well.

Best Gordon

Monday 17-Sep-2018

... by: Cenoman

Hi Gordon,
The name "Almost pattern x" is widely used on sudoku forums. I have no reference specific to "Almost Skyscraper", I learnt using almost patterns while reading solutions of other players.
You could read Steve K's blog page on "Almost finned swordfish example" here:
Very old stuff !
In the actual puzzle, "almost" means that there are additional candidates 4, beside the usual four candidates of a skyscraper, preventing the strong link 4C8=4C1 to exist, namely 4C56.
Through the chain (48-9)C56 = C4 - J4 = (9-4)J8, 4C56 is conflicting with 4J8 (the target of the skyscraper)
Therefore, in English:
WHETHER 4C56 OR skyscraper (4)C8=C1-G1=G9; in both cases J8<>4
It works like a finned fish. 4C56 would be called a "remote fin" (need of a chain)

Another presentation of the elimination is:
||(4)C1 - G1 = G9
||(48-9)C56 = C4 - J4 = (9)J8
=> -4 J8
where the first two chains are a "kraken" presentation of the skyscraper.

In my chain (1)F8 = C8 - ^C4 = DF4* - E56 = E12** - DF3 = AB3 =>-1F56*, -1F2**, -1C2^
the characters *, **, ^ are used to point to the subchains used for each elimination.
(1)F8 = C8 - C4 = DF4 => -1F56
(1)F8 = C8 - C4 = DF4 - E56 = E12 => -1F2
(1)C4 = DF4 - E56 = E12 - DF3 = AB3 => -1C2
Regards, Cenoman

Monday 17-Sep-2018

... by: numpl_npm

J1=4, J3=4 or J8=4 --> J2=6
A3=1, B3=1, D3=1 or F3=1 --> G9=4
D8=1, D8=2 or D8=9 --> A6=5
The rest can be solved.

Sunday 16-Sep-2018

... by: ghfick

Hi Cenoman,

I am not familiar with an 'Almost Skyscraper'. Could you point us to a link that explains its logic and origins? Or better, let us about it here?
Also can you explain your use of *, ** and ^ in your chains?


Sunday 16-Sep-2018

... by: Neil

Hi Vinny and Manny,

In your solution, you only need the 1 and 3 in Box 7, and then the 2 in row 9, col 1.

Best regards,


Sunday 16-Sep-2018

... by: Cenoman

This puzzle has a Jexocet pattern, detected by Andrew's solver, but not completely used.
Following David P Bird's JExocet Compendium:
1. JExocet (1234)JE2: C1,B4,A8
Eliminations (with #n, elimination rule number inDPB's compendium:
-9B4 (non-base digit in target cell; #3)
-1B4 (1 can't be true in the mirror node A79; #6)
-45A9 (A7=6 =>A9 restricted to base digits in B4; #7)
-9B56 (locked 6@B56; #9)
Basics: A6=5, C79=57, -9C8

From there, the puzzle is solved with three AICs & Basics
2. Almost Skyscraper [(4)C8*=C1-G1=G9] = (48-9)C56 = C4 - J4 = (9)J8 => -4 J8
Basics: G9=4, G7=5=C9, C7=7, J48=39, J2=6, ABH9=239, E9=6, DF1=68, J1=5, J3=4=C1, A8=4, B56=46, -2H1
3. (3=2)B4 - (2=1)A5 - (1=8)G5 - C5 = (8-3)C6 = (3)GH6 =>-3J4
Basics: J4=9, J8=3=E7, C56=89, -9F8, D8=9, -3G2
4. (1)F8=C8 - ^C4 = DF4* - E56 = E12** - DF3 = AB3 =>-1F56*, -1F2**, -1C2^; Basics to the end.

Saturday 15-Sep-2018

... by: Vinny & Manny

Spread 213564 across the empty squares in box 7 (from top left to lower right). Work (hard!) with that for a bit. Enter 23879, top to bottom, along the [at that point] empty cells of col 9. That should lead to the solution.
Vinny & Manny

Saturday 15-Sep-2018

... by: Frans Goosens

With trial and error

Combination D3=125 and H7=239

D3=1 H7=2 No solution, Fixed

Calculate 2 digits cells

D7=7 No solution, Undo calculation
D7=9 Wrong, Undo calculation
D7=7 No solution, Fixed
D8=2 No solution, Undo calculation
D8=9 No solution, Undo calculation
G2=2 No solution, Undo calculation
G2=3 Wrong, Undo calculation
G2=2 No solution, Fixed
D8=2 No solution, Undo calculation
D8=9 Wrong, Undo calculation
D8=2 No solution, Fixed
A5=2 Wrong, Undo calculation
A5=4 Wrong, Undo calculation

All reset to initial position

D3=1 H7=3 No solution, Fixed

Calculate 2 digits cells

D8=2 Wrong, Undo calculation
D8=9 Wrong, Undo calculation

All reset to initial position

D3=1 H7=9 No solution, Fixed

Calculate 2 digits cells

D4=2 Wrong, Undo calculation
D4=5 No solution, Fixed
D6=6 Wrong, Undo calculation
D6=9 Wrong, Undo calculation

All reset to initial position

D3=2 H7=2 No solution, Fixed

Calculate 2 digits cells

D8=1 No solution, Undo calculation
D8=9 No solution, Undo calculation
G5=1 No solution, Undo calculation
G5=8 No solution, Undo calculation
G7=3 Wrong, Undo calculation
G7=5 No solution, Fixed
G9=3 Wrong, Undo calculation
G9=4 ( I3=4 ) Solved,

980 700 600-------------983 715 642
750 000 080-------------751 246 983
006 000 000-------------426 398 715

040 030 000-------------642 537 198
007 800 050-------------197 824 356
000 000 400-------------835 169 427

009 600 070-------------219 683 574
078 450 060-------------378 451 269
000 002 001-------------564 972 831

Total solving time is: 441 sec.


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