The New Sudoku Players' Forum

[syxQn]

A friend brought me a "very hard" sudoku,
and ive learned most of the techniques, but i sense i need some other method
in order to solve this sudoku.
i'd like you guys to direct me to the specific technique in which i have something to work with.
regards, syxqn.

[pjb]

I can't see your puzzle image

phil

[JasonLion]

Here is a more easily accessed copy of the image.

obnhtjwu13yq.png (104.87 KiB) Viewed 1754 times

8..........36......7..9.2...5...7.......457.....1...3...1....68..85...1..9....4..

[pjb]

It certainly is a hard one. However, it has rank zero logic which will result in a reduction of 53 candidates:

16 Truths = {1368R3, 1368R4, 1368R5, 1368R9}
16 Links = {136c1, 6c3, 38c4, 8c8, 136c9, 3n6, 4n5, 4n7, 5n2, 9n5, 9n6}
23 Eliminations: 36<>4, 45<>2, 47<>9, 52<>2, 95<>2, 95<>7, 96<>2, 13<>6, 14<>3, 19<>1, 19<>3, 19<>6, 21<>1, 28<>8, 29<>1, 61<>6, 63<>6, 69<>6, 71<>3, 74<>3, 81<>3, 81<>6, 89<>3
then
Naked quads of 4579 at r1c8, r1c9 and r2c8 and r2c9
5s at r3c1 and r3c3 only ones in row.
Naked triplets of 249 at r1c3, r2c1 and r2c2
Puzzle state after this:

Code: Select all

8      16     249    | 27     12357  123    | 36     4579   4579   
249    24     3      | 6      2578   28     | 1      4579   4579   
156    7      56     | 4      9      13     | 2      8      36     
---------------------+----------------------+---------------------
123469 5      2469   | 2389   368    7      | 68     249    12469 
12369  1368   269    | 2389   4      5      | 7      29     1269   
2479   2468   2479   | 1      268    2689   | 5689   3      2459   
---------------------+----------------------+---------------------
2457   234    1      | 279    237    2349   | 359    6      8     
247    2346   8      | 5      2367   23469  | 39     1      279   
23567  9      2567   | 2378   1368   1368   | 4      257    2357   


Alternatively, use could use the following multi-segment locked sets rank zero logic with same eliminations:
Base: 1368
20 Cell Truths: r12678 c2567
20 links: 136r1, 18r2, 68r6, 3r7, 36r8, 24c2, 257c5, 249c6, 59c7

After this, there is still a lot of hard work to do with complex chains.
Good luck,
Phil

PS there are voluminous threads on these rank zero techniques in the "advanced techniques" section

[daj95376]

Your "friend" has pulled a dirty trick on you. When a solution needs Multi-Sector Locked Sets, then it needs a computer and not a manual solution.

Even when your grid is analyzed for 4-value Template combinations, the results don't reduce the puzzle to where basic techniques will finish solving it. Specifically, there are only 20 template combinations for the digits <1368> that don't result in a contradiction. These 20 combinations result in the following eliminations.

Code: Select all

 <1368>        accepted = 20 template combinations

 <1368>   <>1  r1c79,r2c12569,r3c9,r4c7               i.e., r2c7=1
 <1368>   <>3  r1c49,r3c4,r5c2,r7c146,r8c169,r9c15
 <1368>   <>6  r1c39,r4c137,r5c1,r6c139,r8c12,r9c56
 <1368>   <>8  r2c78,r3c46,r4c458,r5c8,r6c7           i.e., r3c8,r4c7=8

 <1368>        r1c27,r2c7,r3c689,r4c579,r5c124,r6c2,r9c56   locked for candidates

 <1368>   <>2  r1c2,r4c59,r5c124,r6c2,r9c56
 <1368>   <>4  r1c2,r3c689,r4c9,r6c2
 <1368>   <>5  r1c7,r2c7,r3c89
 <1368>   <>7  r9c5
 <1368>   <>9  r1c7,r2c7,r4c79,r5c14


Code: Select all

 resulting grid after the above eliminations and Simple Sudoku Technique Set
 +-----------------------------------------------------------------------+
 |  8      16     249    |  7      135    123    |  36     459    459    |
 |  249    24     3      |  6      58     28     |  1      4579   4579   |
 |  156    7      56     |  4      9      13     |  2      8      36     |
 |-----------------------+-----------------------+-----------------------|
 |  12349  5      249    |  239    36     7      |  8      249    16     |
 |  13     168    269    |  38     4      5      |  7      29     1269   |
 |  2479   68     2479   |  1      268    69     |  569    3      2459   |
 |-----------------------+-----------------------+-----------------------|
 |  2457   234    1      |  29     237    49     |  359    6      8      |
 |  247    234    8      |  5      2367   469    |  39     1      279    |
 |  2567   9      2567   |  238    18     138    |  4      257    2357   |
 +-----------------------------------------------------------------------+
 # 104 eliminations remain


[JC Van Hay]

This is the 12th and the last Arto Inkala's puzzle: "AI Efamol" (SE=10.7). It is the easiest puzzle of the series to solve manually because of the step #1.

From my archive :

Note : C(S)=Contradiction using only Singles

Code: Select all

+--------------------------+-------------------------+-------------------------+
| 8         1246    2459-6 | 247-3   12357    1234   | 13569  4579    4579-136 |
| 2459-1    124     3      | 6       12578    1248   | 1589   4579-8  4579-1   |
| (1456)    7       (456)  | (348)   9        138-4  | 2      (458)   (13456)  |
+--------------------------+-------------------------+-------------------------+
| (123469)  5       (2469) | (2389)  368-2    7      | 168-9  (2489)  (12469)  |
| (12369)   1368-2  (269)  | (2389)  4        5      | 7      (289)   (1269)   |
| 2479-6    2468    2479-6 | 1       268      2689   | 5689   3       2459-6   |
+--------------------------+-------------------------+-------------------------+
| 2457-3    234     1      | 2479-3  237      2349   | 359    6       8        |
| 247-36    2346    8      | 5       2367     23469  | 39     1       279-3    |
| (23567)   9       (2567) | (2378)  1368-27  1368-2 | 4      (257)   (2357)   |
+--------------------------+-------------------------+-------------------------+


#1. Rank 0 All Cells : R3459C13489 :=> -1368r12678c13489, -2479r3459c2567
HP(36-1459)r1c3,r3c9; r2c7=1,r3c8=8; UP23; LC(5r3c13)-5r13c13; HT(156-24)r1c3,r2c12; r3c4=4;UP24
#2. r3c1=1or5->C(S) :=> r3c1=6; 7 Singles; UP32; HP(16-249)r45c9
#3. r4c5=6->C(S) :=> r4c5=3; UP81

[syxQn]

Hey guys, i rally appreciate the help with the data youre giving me, but
Im working (imo) and worked with easier sudokus.
I actually wanted you guys to address me to which specific technique
That i need to LEARN. In order to solve this sudoku. Im far from controlling
Those techniques ure talking about. Im not presmptuous, i wanna learn,
this is the reason i was glad to find this site of smart people like you. (-:
In short i need guiding. Thx.

Regards, syxqn.

P.s
I had a feeling that my friend brought me an impossible sudoku.

[JasonLion]

I actually wanted you guys to address me to which specific technique
That i need to LEARN. In order to solve this sudoku. Im far from controlling
Those techniques ure talking about.

That puzzle isn't impossible, but from what you said it sounds like it is way beyond your ability level.

They did tell you which technique you need to learn: rank 0 logic. However that is one of the most complex techniques, one almost never mastered by human solvers and normally only used by computer programs.

You will also need to master nearly all of the solving techniques that are simpler than rank 0 logic in order to tackle that particular puzzle by hand.

Take a look at this page and start working on anything you don't already have mastered.

[999_Springs]

this is the same puzzle that was once claimed to be the "world's hardest sudoku" by arto inkala (2012). if you google search "world's hardest sudoku" then this puzzle comes up

while this puzzle IS really, really, REALLY hard, it is emphatically NOT the world's hardest sudoku by quite a long way, since as you can see there's a multi-fish at the start that kills off a lot of candidates and reduces it to 9.0 se, and arto inkala is a well-known fraud/imposter.

in 2013 i wrote a thingy on another (non-sudoku) forum about arto inkala and the fakeness of the claim, as well as my (manual) solution path. i tried to make both explanations accessible to the layman. have a read through it if you want (i go by "zapmeister" on that forum, my posts start on page two)

[syxQn]

I actually wanted you guys to address me to which specific technique
That i need to LEARN. In order to solve this sudoku. Im far from controlling
Those techniques ure talking about.

That puzzle isn't impossible, but from what you said it sounds like it is way beyond your ability level.

They did tell you which technique you need to learn: rank 0 logic. However that is one of the most complex techniques, one almost never mastered by human solvers and normally only used by computer programs.

You will also need to master nearly all of the solving techniques that are simpler than rank 0 logic in order to tackle that particular puzzle by hand.

Take a look at this page and start working on anything you don't already have mastered.

youre the best, thats exactly what i was lurking for (-:
ill better get starting with it..