How would you solve this (ER 9.2)?

Post the puzzle or solving technique that's causing you trouble and someone will help

How would you solve this (ER 9.2)?

Postby SpAce » Thu Feb 08, 2018 4:56 am

I've been solving sub-9 puzzles consistently without problems, so I finally decided to take a stab at the next level. I picked a low 9.x puzzle randomly from the patterns game, and well, my feeble skills weren't any kind of a match for it :D I got exactly two placements with horrible nets before I gave up. I expected it to be a different game but not this different.

What surprised me more, however, was that even Hodoku couldn't solve it without two brute force moves (I'm pretty sure I've turned on all of its techniques -- Edit: but I was wrong, see below). The SudokuWiki solver couldn't solve it at all. I didn't expect that since the rating was only 9.2. To be exact, it was ED=9.2/9.2/8.9, which might explain the overall difficulty (if I understand those latter numbers correctly), but still, shouldn't Hodoku be able to handle max-9.2-techniques without resorting to brute force?

Anyway, I was wondering if a skilled human (or program) can find some advanced patterns here that would make it solvable without crazy forcing nets (or at least fewer of them)? I know some only by name (JExocet, SK-Loop, etc) and their general principles but have never used any.

Code: Select all
. . 1 | . . . | . . 2
. . 2 | 3 1 . | . 4 .
5 6 . | . . 2 | 7 . .
------+-------+------
. 3 . | . . . | . . .
. 2 . | . . . | 5 . .
. . 7 | . . 1 | . 8 .
------+-------+------
. . 6 | . 5 . | . . 9
. 1 . | . . 4 | . . .
9 . . | . . . | 3 . 4  ED=9.2/9.2/8.9

http://forum.enjoysudoku.com/patterns-game-t6290-35775.html#p263656

Code: Select all
.-------------------.------------------------.--------------------.
| 3478   4789  1    | 456789   46789   56789 | 689    3569   2    |
| 78     789   2    | 3        1       56789 | 689    4      568  |
| 5      6     3489 | 489      489     2     | 7      139    138  |
:-------------------+------------------------+--------------------:
| 1468   3     4589 | 2456789  246789  56789 | 12469  12679  167  |
| 1468   2     489  | 46789    346789  36789 | 5      13679  1367 |
| 46     459   7    | 24569    23469   1     | 2469   8      36   |
:-------------------+------------------------+--------------------:
| 23478  478   6    | 1278     5       378   | 128    127    9    |
| 2378   1     358  | 26789    236789  4     | 268    2567   5678 |
| 9      578   58   | 12678    2678    678   | 3      12567  4    |
'-------------------'------------------------'--------------------'
Last edited by SpAce on Fri Feb 09, 2018 1:09 am, edited 1 time in total.
SpAce
 
Posts: 190
Joined: 22 May 2017

Re: How would you solve this (ER 9.2)?

Postby Leren » Thu Feb 08, 2018 8:16 am

Looks like a brute to me. Couldn't find any JExocets, SK Loops, Multifish or MSLS.

Leren
Leren
 
Posts: 3024
Joined: 03 June 2012

Re: How would you solve this (ER 9.2)?

Postby champagne » Thu Feb 08, 2018 10:19 am

you can have a look at the way Sudoku Explainer solves it, nothing exciting for a manual player.
Many steps in the area 8.9 9.2.
The first steps say

7 r1c1 -> no '4' in box 1
8 r1c1 -> no '4' in box 1
6 r2c9 -> no 8 in column 9 ....
champagne
2017 Supporter
 
Posts: 5866
Joined: 02 August 2007
Location: France Brittany

Re: How would you solve this (ER 9.2)?

Postby 200e200w » Thu Feb 08, 2018 11:03 am

Hi, SpAce!
I used Hodoku at maximal settings and got this result (only techniques used and their frequency + rating of puzzle):
1 x 2-String Kite
1 x Hidden UR
1 x Finned Swordfish
1 x XY-Chain
1 x AIC
1 x Discontinuous Nice Loop
2 x Grouped AIC
12 x Grouped Discontinuous Nice Loop
1 x Kraken Fish Type 1
12 x Kraken Fish Type 2
Score: 12718/10.3
So, it is solvable with only pure and human-friendly logic. Another thing to say, I said here that Hodoku at maximal settings can solve puzzles using only logic even up to ER=9.6.
If you want to try more puzzles with ER~9.0, try Andrew's Weekly Unsolvables or my Top 250. Most of Andrew's Unsolvables and hardest puzzles in my Top 250 are from ~9.0 level, so you will have some fun from solving them (if you will manage to do it...).

200e200w
200e200w
 
Posts: 185
Joined: 20 January 2018

Re: How would you solve this (ER 9.2)?

Postby SpAce » Fri Feb 09, 2018 1:08 am

Thanks Leren and champagne for confirming that I wasn't totally imagining the puzzle's hellish nature. And 200e200w -- thanks for telling me that I sort of was anyway :)

200e200w wrote:Hi, SpAce!
I used Hodoku at maximal settings and got this result (only techniques used and their frequency + rating of puzzle):
...
1 x Kraken Fish Type 1
12 x Kraken Fish Type 2
Score: 12718/10.3

Thanks! Seems that I wasn't using high enough Hodoku options after all.

So, it is solvable with only pure and human-friendly logic.

Pure, yes, but I guess we have a bit different definition of human-friendly logic :D I'd really like to see a human actually solve it using those techniques without computer aids and call it human-friendly. The list would be a bit more descriptive if it showed what kind of kraken fishes were used. I'm not sure if things like Type 2 Kraken Franken Whales with 4 fins etc can be called exactly human-friendly, unless someone shows me how they can be found relatively easily using just pencil and paper. I guess anything can be called a fish if you just add enough fins, which makes finding the useful ones pretty tough, I would imagine.

Another thing to say, I said here that Hodoku at maximal settings can solve puzzles using only logic even up to ER=9.6.

I remembered that, which is why I was puzzled when Hodoku couldn't solve it without brute force. I thought I'd already turned on all options after that discussion, but it turns out I hadn't (or perhaps I'd turned something back off to save time). Thanks for letting me know (again). With untied hands Hodoku did indeed solve this without brute force, but it took a long time. If it takes software that long to solve using those kinds of techniques, how long does it take for a skilled human?

If you want to try more puzzles with ER~9.0, try Andrew's Weekly Unsolvables or my Top 250. Most of Andrew's Unsolvables and hardest puzzles in my Top 250 are from ~9.0 level, so you will have some fun from solving them (if you will manage to do it...).

Thanks for the tip! I will try them, at some point. This one wasn't a particularly encouraging first attempt, though :) I was wondering if there were any 9-level puzzle collections screened for human consumption? I'd still like to get some practice with the harder techniques, but with some milder examples. With my minimal experience it seems like the jump from 8 to 9 is quite huge compared to the gap between 7 and 8. Most of the time I couldn't tell the difference between ER 7.x and 8.x puzzles, but it seems the game changes radically at 9.x. Does that assumption have any merit?
SpAce
 
Posts: 190
Joined: 22 May 2017

Re: How would you solve this (ER 9.2)?

Postby totuan » Sun Feb 11, 2018 12:06 pm

Code: Select all
 *--------------------------------------------------------------------------------------*
 | 3478     4789     1        | 456789   46789    56789    | 689      3569     2        |
 | 78       789      2        | 3        1        56789    | 689      4        568      |
 | 5        6        3489     | 489      489      2        | 7        139      138      |
 |----------------------------+----------------------------+----------------------------|
 | 1468     3        4589     | 2456789  246789   56789    | 12469    12679    167      |
 | 1468     2        489      | 46789    346789   36789    | 5        13679    1367     |
 | 46       459      7        | 24569    23469    1        | 2469     8        36       |
 |----------------------------+----------------------------+----------------------------|
 | 23478    478      6        | 1278     5        378      | 128      127      9        |
 | 2378     1        358      | 26789    236789   4        | 268      2567     5678     |
 | 9        578      58       | 12678    2678     678      | 3        12567    4        |
 *--------------------------------------------------------------------------------------*

An urgly part for this one – hope a better from others:

01: Present as diagram: => r1c8<>9

Code: Select all
(7)r9c6-r2c6=r2c12—-----(7)r1c2
 ||                 |    ||
(8)r9c6-(58=7)r9c23-    (9)r1c2*
 ||                      ||
 ||                     (4)r1c2-r7c2=(4-2)r7c1=(2)r8c1-(2=689)r128c7*
 ||                      ||     
 ||                     (8)r1c2-(8=7)r2c1-(7)r8c1
 ||                                        ||
(6)r9c6-(6)r8c45                          (2)r8c1-(2=689)r12c7*
         ||                                ||
        (6)r8c7-(6=89)r12c7*              (3)r8c1-r1c1=r1c8* 
         ||                                ||   
        (6)r8c8-(5)r8c8                   (8)r8c1-r8c9=r23c9-(8=69)r12c7* 
         ||      ||
         ||     (5-3)r8c3=r3c3-r1c1=r1c8*
         ||      || 
         ||     (5-8)r8c9=r23c9-(8=69)r12c7*
         ||
        (6-8)r8c9=r23c9-(8=69)r12c7*


From here it’s not hard to downgrade the puzzle based on Almost X-wing 9’s on r68, I’m lazy to complete it :D :D :D

totuan
totuan
 
Posts: 5
Joined: 25 May 2010
Location: vietnam

Re: How would you solve this (ER 9.2)?

Postby SpAce » Mon Feb 12, 2018 10:38 am

totuan wrote:
Code: Select all
(7)r9c6-r2c6=r2c12—-----(7)r1c2
 ||                 |    ||
(8)r9c6-(58=7)r9c23-    (9)r1c2*
 ||                      ||
 ||                     (4)r1c2-r7c2=(4-2)r7c1=(2)r8c1-(2=689)r128c7*
 ||                      ||     
 ||                     (8)r1c2-(8=7)r2c1-(7)r8c1
 ||                                        ||
(6)r9c6-(6)r8c45                          (2)r8c1-(2=689)r12c7*
         ||                                ||
        (6)r8c7-(6=89)r12c7*              (3)r8c1-r1c1=r1c8* 
         ||                                ||   
        (6)r8c8-(5)r8c8                   (8)r8c1-r8c9=r23c9-(8=69)r12c7* 
         ||      ||
         ||     (5-3)r8c3=r3c3-r1c1=r1c8*
         ||      || 
         ||     (5-8)r8c9=r23c9-(8=69)r12c7*
         ||
        (6-8)r8c9=r23c9-(8=69)r12c7*


Wow! That's a pretty cool net :) With your notation it's surprisingly understandable, too! I'm just wondering... how do you actually find such beasts? I've understood that you're a master of these kinds of net solutions, so I guess you must have a method for it.

Btw, is there an 8 missing here: (2)r8c1-(2=689)r128c7* ?
SpAce
 
Posts: 190
Joined: 22 May 2017

Re: How would you solve this (ER 9.2)?

Postby 200e200w » Sat Feb 24, 2018 5:00 pm

Good news to you, SpAce!
There are 9.x puzzles for which the hardest required techniques according to Hodoku are AIC's. These are 2 examples of them, with SE rating at the end of the line:
.4..1.2.......9.7..1..........43.6..8......5....2.....7.5..8......6..3..9........ (ER=9.2)
....4...1.3.6.....8........1.9..5.........87....2......7....26.5...94.........3.. (ER=9.0)
Try them - with your skills I'm sure you'll solve them.

200e200w
200e200w
 
Posts: 185
Joined: 20 January 2018


Return to Help with puzzles and solving techniques