... by: mabarbee

#670 automatic solve:
Solution order =
* = successful guess
A42,G55,G49*,G78*,B47*, and solve.
Solve time 3 ms.

Please do not consider the following to be boasting. I only want to make contact with someone who has also developed a working solver for purposes of collaboration and learning. This information is provided with the intent that I might raise the interest of a like-minded developer.

My solver will solve any valid (one solution) puzzle in the world. It is impossible for it to output an incorrect solution. It has never failed on any "Weekly Unsolvable".
It easily solved all 10 of Arto Inkala's "World's Hardest" in less than 1/2 second total for the batch file with all 10. (I only count time from puzzle loaded in memory until puzzle last square. Not I/O). If anyone is interested in looking at my code or might be interested in collaborating on advanced strategy enhancements, please let me email me at mbarbee3741@gmail.com I would definitely like to take a look at your solver code. I am interested in possibly adding map reduction to my algorithms. Also, more advanced strategies. And I would like to learn about graphical implementation. Sorry if this seems strange. My social skills are poor. I am on the autistic spectrum. Thank you for reading this. I hope someone will email me.

... by: mabarbee

Hello Franz. Very impressed with A6=3 ( H3=5 ) Solved!!

I inserted those two into my solver and it was able to go straight through to the end with 0 guesses. Here is the run with solution order after the insertion of your 2 clues:

C:\Users\mabarbee\Desktop\desktop\sudoku projects>copy "weeklynov7temp.txt" i.txt
1 file(s) copied.

C:\Users\mabarbee\Desktop\desktop\sudoku projects>solver
GLTIME2=1762511638030166
GLTIME1=1762511638030166
GELAPSEDTIME=0
=====================================================

468 293 157
912 785 346
357 416 928

236 548 791
849 172 635
571 369 284

624 951 873
195 837 462
783 624 519

puzzle type=manual input
elapsed time < 500 microseconds
# initial clues=25
guesscount=0
# solved before first guess=56
# solved squares=56

Solution order =
* = successful guess
B73,A42,G55,D68,A38,
A14,B58,I75,F15,A85,
C25,I28,I33,A97,A71,
D91,F94,I64,H92,G22,
G34,D12,B19,B21,B47,
I17,H11,I99,C37,B96,
G49,H86,H67,I46,G61,
G87,G78,F88,E41,C66,
C82,C51,F72,F43,E76,
C79,D36,F56,E57,E39,
D54,F27,E24,D89,D23,
E83

... by: BGH

Dieter's Method
Just for grins, I added a digit counter to my Sudoku toolkit.
More of a "fiddle" than anything else. Curiosity...

... by: Serban

# 670 A4=2 G5=5 Basics to 25
1. C3=7 solve
2. J1=7 & J2=8 solve
3. H6=7 & J6=4 solve
4. H6=7 & G6=1 solve
5. E5=7 & F5=6 solve

... by: BGH

Thx Dieter

Goosen's solution seems to be the most elegant.

... by: Frans Goosens

#670

Combination 2-digits cells

A6=3 ( H3=5 ) Solved,

Total solving time is : 5 sec.

... by: Dieter

@BGH: Thank you for your comments
After basics A4=2; G5=5 we have 25 cells populated.
A7 then has 3 possible numbers: 1, 3, 5, A3 has 4, 5, 6, 8
I try to get most of the 7 numbers "covered" by two cells, e. g. 5 is covered by both.
It's not an exact mathematical approach and it takes some time to find two cells.
This week I found them very quickly.
Hope this helps a little.

... by: BGH

Dieter, could you explain how 1 & 7 are in your "occurs most frequently" two cell combinations
And how the 1 @ A7 is in your "occurs most frequently" two cell combinations.
I really want to try your method but can't understand 1 & 7 ??

D: Strategy: Numbers 5,3,4,8,9 occur most frequently, combine two cells.
combinations of A3 = (4,5,7,8) and A7 = (1,3,5)
A3=8 & A7=1 solve"

And BTW, I confirmed my solution (5 @ A8) and 2 @ F7 did not solve the grid after 3 @ A6 and
8 @ F8. You can do 2 @ F7 then 5 @ A8 to solve but that makes *4* steps. Anyway, not important. Answer to 1 paragraph would be interesting.

... by: Serban

# 670 A4=2 G5=5 Basics to 25
1.Number 1 n=2 e=7 N=23 Nc=10 Ns=5 => C5=1 solve
2. Number 6 n=2 e=7 N=20 Nc=57 Ns=34 => C6=E7=6 solve
3. Number 2 n=4 e=5 N=17 Nc=9 Ns=3 => F7=2 basics to 47

3a. F7=2 & any[ E4,C5]=1 solve
3b. F7=2 & any[D2,E7]=3 solve
3c. F7=2 & any[E2,D5]=4 solve
3d. F7=2 & any[F1,C2,H3,A8,J7]=5 solve
3e. F7=2 & any[E7,H8,F5,J4]=6 solve
3f. F7=2 & any[J1,E5]=7 solve
3g. F7=2 & any[D8,J9]=9 solve

... by: Envy E

Begin where Solver runs out of known solutions

+1 B4 +1 C2 +2 G2

+1 E4 +1 D9 +4 F9 +2 H9 +2 G2

+1 G4 +2 G2

With G2 set to 2 puzzle is solvable

... by: Dieter

@BGH:
3 @ A6 OK
8 @ F8 OK
5 @ F7 nOK; F7=2

... by: BGH

3 Step Solution to #670
Basics 30.7
3 @ A6 43.2 Cell Pair, Unit Pairs 8’s, Solves for all 8’s except URec
8 @ F8 45.7 Unique Rectangle
5 @ F7 Solution, Solves for all 5’s

Dieter's solution works & matches my solution

... by: Dieter

#670 - initially populated cells: 23 = 28,4%
No solver used.
basics: A4=2; G5=5
populated cells: 25= 30,9%
Strategy: Numbers 5,3,4,8,9 occur most frequently, combine two cells.
combinations of A3 = (4,5,7,8) and A7 = (1,3,5)
A3=8 & A7=1 solve.

... by: Serban

# 670 A4=2 G5=5 Basics to 25

1. Box 4 ABC456 n=4 e=5 Nc=12 Ns=2 => B4=7 & [C5=1 OR C6=6] solve

2. Box 6 GHJ456 n=4 e=5 Nc=10 Ns=5 => G6=1 & H6=7 solve

3. Number 4 n=3 e=6 N=20 Nc=17 Ns=3 => D5=G3=4 solve
Note: A1=G3=J6=4