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Monday 10-Dec-2018

... by: Tokay

2 guesses:

Row Col Val
0 0 7
0 2 2

Sunday 2-Dec-2018

... by: Marion Barbee

My solver had to guess these two squares to solve this one:
================puzzle insert successful=============
row=5 col=7 value=7
================puzzle insert successful=============
================puzzle insert successful=============
row=6 col=5 value=6
================puzzle insert successful=============

Sunday 2-Dec-2018

... by: Marion Barbee

C:\Users\John\Desktop\sudoku>solver
=====================================================

792 684 531
561 392 478
843 157 296

437 521 869
916 843 725
258 769 314

184 276 953
675 938 142
329 415 687

puzzle type=MANUAL_INPUT
Elapsed time is: 9 milliseconds

That was as quick as I could get it done in 4 tries.

Sunday 2-Dec-2018

... by: Marion Barbee

792 684 531
561 392 478
843 157 296

437 521 869
916 843 725
258 769 314

184 276 953
675 938 142
329 415 687

puzzle type=MANUAL_INPUT
Elapsed time is: 53 milliseconds

Sunday 2-Dec-2018

... by: Daniel Cohen

No worries, Bob. So the step count was a little bit high for this solve. I believe it is counting the execution of a solving strategy a step, whether it finds an elimination or not. Since the strategy list by default is quite long, and Forcing Nets by default are the last strategy checked before resorting to Trial and Error, this particular solve did have a relatively high step count.

Saturday 1-Dec-2018

... by: BobW

Sorry Daniel. I called you David by mistake.

Saturday 1-Dec-2018

... by: BobW

Hi David. Thanks for your solution. May I ask how you calculate the number of steps? 2384 seems fairly high for a non-T&E solver. I went back and added some additional statistics tracking to my partial-T&E solver, and it comes up with a step count of 2038 for this puzzle, but we may be using different definitions of what a step is. My solver increments the step count whenever a candidate is eliminated from a cell, even if it's in a dead end branch that later gets pruned.
Other stats for this puzzle with my solver:
Total times a specific pattern is searched for: 375
Total times a pattern is found even if it doesn't result in a candidate removal: 9187
Total times a pattern is found that results in at least one candidate removal: 171
All of the above totals include instances that occur in pruned branches.

Saturday 1-Dec-2018

... by: Daniel Cohen

Without any trial and error:

Box/Line Reduction
Finned X Wings
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Pointing Pairs
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Forcing Net Contradiction
Hidden Pairs
Alternating Inference Chains
Alternating Inference Chains
Nishio Forcing Chains
Nishio Forcing Chains
Unit Forcing Chains
Forcing Net Contradiction
Forcing Net Contradiction
Pointing Pairs
Forcing Net Contradiction
Finned X Wings
Forcing Net Contradiction
Forcing Net Contradiction
Naked Triples
Hidden Unique Rectangles
Nishio Forcing Chains
Unit Forcing Chains
Forcing Net Contradiction
Pointing Pairs
Miscellaneous Chains
Miscellaneous Chains
Pointing Pairs
Box/Line Reduction
Forcing Net Contradiction
X Wings
Almost Locked Candidates
Almost Locked Sets XZ
Hidden Triples
Finned X Wings
Almost Locked Sets XZ
Alternating Inference Chains
Swordfish
Aligned Pair Exclusion
Sashimi X Wings
Alternating Inference Chains

solver result = SUDOKU_SOLVED
step count = 2384

7 9 2 6 8 4 5 3 1
5 6 1 3 9 2 4 7 8
8 4 3 1 5 7 2 9 6
4 3 7 5 2 1 8 6 9
9 1 6 8 4 3 7 2 5
2 5 8 7 6 9 3 1 4
1 8 4 2 7 6 9 5 3
6 7 5 9 3 8 1 4 2
3 2 9 4 1 5 6 8 7

Saturday 1-Dec-2018

... by: numpl_npm

+5C5 +9H4 +7G5 ( by Andrew's Solver with basics )

-4G6 ( by Andrew's Solver with basics, Altern. Inference Chains only )
So +4J4.

-6J5 ( by Andrew's Solver with basics, Altern. Inference Chains )
-5E3 ( by Andrew's Solver with basics, Altern. Inference Chains, Almost Locked Sets )
So +6E3.

-8J5 ( by Andrew's Solver with basics, Altern. Inference Chains )
So +1J5.

To solution ( by Andrew's Solver with basics, Altern. Inference Chains )

Saturday 1-Dec-2018

... by: numpl_npm

+5C5 +9H4 +7G5.
-2F5 -2D6 -1A5 ( By Andrew's Solver without Bowman's Bingo ).
So +2D5 +8A5.
And no longer unsolvable.

Saturday 1-Dec-2018

... by: Frans Goosens

With trial and error

Combination A5=128 and G9=358

************************************************************
A5=1 G9=3 Wrong, Undo calculation

All reset to initial position

************************************************************
A5=1 G9=5 Wrong, Undo calculation

All reset to initial position

************************************************************
A5=1 G9=8 Wrong, Undo calculation

All reset to initial position

************************************************************
A5=2 G9=3 Wrong, Undo calculation

All reset to initial position

************************************************************
A5=2 G9=5 Wrong, Undo calculation

All reset to initial position

************************************************************
A5=2 G9=8 No solution, Fixed

Combination 2-digits cells

C4=1 Wrong, Undo calculation
C4=8 Wrong, Undo calculation

All reset to initial position

************************************************************
A5=8 G9=3 ( D9=9 ) Solved,


#324--------------------------Solution
000 600 500-------------792 684 531
060 090 070-------------561 392 478
003 007 006-------------843 157 296

400 500 800-------------437 521 869
010 040 020-------------916 843 725
008 009 004-------------258 769 314

100 200 900-------------184 276 953
000 030 040-------------675 938 142
009 005 007-------------329 415 687

Total solving time is: 145 sec.

Saturday 1-Dec-2018

... by: Daniel Cohen

Hello, everyone! My name is Daniel Cohen. Please enjoy solving this puzzle I generated. I think it is very difficult. My solver is able to solve it, but resorts to a specialized version of Forcing Net 25 times during the solution. I am very curious to see how you all go about solving it. Have fun! Thanks, Dan

Saturday 1-Dec-2018

... by: BobW

Hi Everyone,
Over the past few months I've been building my own solver program to help me improve my manual solving skills. Last week I added a trial and error routine to the solver for when the logic strategies are exhausted, so it will now solve the unsolvables. Here is the summary output for this week's puzzle.


Summary (Combining Trial & Error with Logic Strategies):

792 684 531
561 392 478
843 157 296

437 521 869
916 843 725
258 769 314

184 276 953
675 938 142
329 415 687

Final Cell Values by Solve Order:

Initial Values:
A4=6, A7=5, B2=6, B5=9, B8=7, C3=3, C6=7, C9=6, D1=4, D4=5, D7=8, E2=1, E5=4, E8=2, F3=8, F6=9, F9=4, G1=1, G4=2, G7=9, H5=3, H8=4, J3=9, J6=5, J9=7
Solved:
C5=5, H4=9, G5=7, *E3=6, *E6=3, E7=7, E4=8, B4=3, F4=7, *E1=9, E9=5, G8=5, G3=4, G6=6, J4=4, C4=1, *J5=1, H6=8, D6=1, A5=8, *A1=7, *A2=9, C2=4, C7=2, C1=8, C8=9, H9=2, A6=4, B6=2, B7=4, J8=8, J2=2, F2=5, H2=7, H3=5, H1=6, H7=1, J1=3, J7=6, F7=3, D8=6, D5=2, D3=7, F5=6, F8=1, A8=3, A9=1, A3=2, B9=8, B1=5, D9=9, F1=2, G2=8, B3=1, D2=3, G9=3
* Asterisk indicates trial & error assignment used when all logic strategies have been exhausted.

Deepest recursion: 8
Unlimited depth search Backdoor values: E3=6 E6=3 E1=9 J5=1 A1=7 A2=9

Total solution time: 560.88 milliseconds

Minimal backdoor: A1=7 H3=5

No single cell backdoor found.

Archive

Each week a new 'unsolvable' will be published and the previous will be accessible here from this archive section. If you like very tough puzzles, these are for you.
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