The New Sudoku Players' Forum

[Jasper32]

This is a puzzle that really seems tough, at least to me. I have seen where puzzles are graded with something like, 8.3, 8.4, etc. I wonder where I should go to get this puzzle graded.

This is not the reason for the post. I have reached an impasse as to what the next step in solving this puzzle might be. Probably the next couple of steps, as I mentioned before it seems very difficult to me. Of course, maybe I have missed something that is rather obvious and you will find it fairly simple to complete.

The first puzzle below is the original puzzle and the one below that is where I “hit the wall.”

Thank you so much for your help.

Code: Select all

 *-----------*
 |3.4|..1|...|
 |..8|.6.|...|
 |59.|8..|...|
 |---+---+---|
 |..5|1.2|..7|
 |.2.|...|.3.|
 |4..|7.6|8..|
 |---+---+---|
 |...|..7|.96|
 |...|.4.|3..|
 |...|6..|1.5|
 *-----------*



Code: Select all

 *--------------------------------------------------------------------*
 | 3      67     4      | 259    2579   1      | 279    568    289    |
 | 127    17     8      | 34     6      59     | 2579   125    34     |
 | 5      9      1267   | 8      27     34     | 267    126    34     |
 |----------------------+----------------------+----------------------|
 | 69     8      5      | 1      3      2      | 469    46     7      |
 | 679    2      679    | 459    589    4589   | 569    3      1      |
 | 4      13     13     | 7      59     6      | 8      25     29     |
 |----------------------+----------------------+----------------------|
 | 8      345    23     | 235    1      7      | 24     9      6      |
 | 12679  1567   12679  | 259    4      589    | 3      278    28     |
 | 279    347    2379   | 6      289    389    | 1      2478   5      |
 *--------------------------------------------------------------------*



[storm_norm]

ttt,
thanx.
I now see my error.

[StrmCkr]

Sudoku Explainer rates puzzles

found here

http://diuf.unifr.ch/people/juillera/Sudoku/Sudoku.html

some take hours... anything thats beyond a 9...

this one is 8.4
(on SE version 1.2.1)

[DonM]

Jasper32, I'm wondering where you are getting these puzzles? Usually, there is some indication of the difficulty of a puzzle if it's from a newspaper, sudoku book or even from an internet site. In any event, while some of us find it an interesting challenge to solve puzzles in this difficulty range, in all honesty, I don't think you're going to be helped by the sort of solutions we come up with for a puzzle like this.

In all honesty, the best way to move ahead in solving is to start with puzzles of a given difficulty level (ie. you should know before solving a puzzle what it's difficulty level generally is) and master those before moving on. For instance, some time ago for me, one landmark was the newspaper diabolicals (or whatever name is given to the most difficult newspaper sudoku of the week in your area). Once I could reliably solve those, then I started trying some of the 'easier' extremes such as those of ER=7.1 to 7.3 range although even they can be a challenge. Long story short, one thing I can tell: only a relative handful of people on either of the main forums can manually solve an ER=8.4 puzzle.

[Jasper32]

Hi DonM, To answer where the puzzle came from was off the web at www.stricklysudoku.com and they have four levels of difficulty for their puzzles: easy, medium, hard and fiendish. I have solved many, many of the fiendish puzzles with no difficulty. There is no rating on the fiendish puzzles so you cannot tell just how fiendish, fiendish is. The reason for posting this puzzle was I thought that perhaps I had overlooked something that would help me in the future. I don’t try to rate a puzzle, I accept it as it published.

After reading your post, I entered the puzzle in the Scanraid Solver and it couldn’t rate it because of it’s complexity. It did solve the puzzle, however it used a Bowman Bingo and ton’s of ALS’s as well as a Death Blossom and then just more or less everyday strategies.

I am well aware of ALS’s but have a difficult time locating them and have never heard of an easy way to find them. Even with the ALS’s, that alone would not have solved the puzzle.

Then I went to the site referred to by “Strmckr” which is “Sudoku Explainer”. I ran the puzzle through that solver as well. It solved the puzzle by mostly, and I mean mostly, using Forcing Chains which were so complicated that even a Rhodes Scholar or a member of Mensa could not have deciphered them unless they possessed a magic decoder ring.

Before I post any more puzzles, I will get a rating for them first. My sincere apologies if I violated a protocol that I was totally unaware of. That was not my intention.

BTY, I could not rate this puzzle with “Sudoku Explainer”. I will revisit that site and try again. It that the only site that gives the rating such as “ER 8.4”. Since this seems to be how forum members rate puzzles, I would like to be grade a puzzle in that fashion.

Thanks to all of you for your replies.

[DonM]

I am well aware of ALS’s but have a difficult time locating them and have never heard of an easy way to find them. Even with the ALS’s, that alone would not have solved the puzzle.

You're right, it wouldn't.

Then I went to the site referred to by “Strmckr” which is “Sudoku Explainer”. I ran the puzzle through that solver as well. It solved the puzzle by mostly, and I mean mostly, using Forcing Chains which were so complicated that even a Rhodes Scholar or a member of Mensa could not have deciphered them unless they possessed a magic decoder ring.
Before I post any more puzzles, I will get a rating for them first. My sincere apologies if I violated a protocol that I was totally unaware of. That was not my intention.

No, don't misunderstand- there was no protocol violated. Just trying to set you on the best path for your own solving. You might want to try running those fiendish puzzles thru SE to get a rating before you try solving them and initially restrict yourself to puzzles in the <8 range. Also, it is helpful for us to know the SE rating so at least we know what we're dealing with. Otherwise, we're always here to help & we actually tend to enjoy it...far more often than not...

BTY, I could not rate this puzzle with “Sudoku Explainer”. I will revisit that site and try again. It that the only site that gives the rating such as “ER 8.4”. Since this seems to be how forum members rate puzzles, I would like to be grade a puzzle in that fashion.

I've never come across a puzzle that SE wouldn't give a rating on. The best way to use it is to download SE itself from here:

http://diuf.unifr.ch/people/juillera/Sudoku/Sudoku.html

Download the zip file version because it contains the Java Runtime. This is about as easy a program to install as possible: Simply unzip it to a folder & it is ready to run (make sure to select the unzip option to restore folders)- there is no actual installation to Windows itself. However, you might be tripped up by the fact that SE isn't particularly intuitive. To get the rating, first enter the puzzle to the grid by clicking on each cell (turns brown) and entering the number from your keyboard, then click on Tools above and select Analyze from the bottom of the drop-down box. The only evidence that anything is happening is the presence of the hour-glass icon. The result will appear in the bottom right corner opposite 'Hint rating:' (not necessarily the best term methinks...).

If it's a puzzle under 8, the result will come up fairly quickly. If the puzzle is anywhere above 8.7, it will take noticeably longer. Note that you can enter F9 directly to activate Analyze w/o going to Tools, but for some reason, there is no hour-glass to indicate that the program is working on the rating and it will not appear that anything is happening...but it is, just be patient.

[ttt]

Code: Select all

 *--------------------------------------------------------------------*
 | 3      67     4      | 259    2579   1      | 279    568    289    |
 | 127    17     8      | 34     6      59     | 2579   125    34     |
 | 5      9      1267   | 8      27     34     | 267    126    34     |
 |----------------------+----------------------+----------------------|
 | 69     8      5      | 1      3      2      | 469    46     7      |
 | 679    2      679    | 459    589    4589   | 569    3      1      |
 | 4      13     13     | 7      59     6      | 8      25     29     |
 |----------------------+----------------------+----------------------|
 | 8      345    23     | 235    1      7      | 24     9      6      |
 | 12679  1567   12679  | 259    4      589    | 3      278    28     |
 | 279    347    2379   | 6      289    389    | 1      2478   5      |
 *--------------------------------------------------------------------*

From your grid, I found 2 moves that’s quite interested:

01: (1=7)r2c2-(7)r9c2=[XY-wing (234): r9c2, r7c3, r7c7]-(4)r7c2=(4)r7c7-(4)r4c7=(4-6)r4c8=(6)r13c8-(6)r3c7=(hp16-2)r3c38=(2)r2c1 => r2c1<>1, r8c1=1
02: (7)r9c2=[XY-wing (234): r9c2, r7c3, r7c7]-(4)r7c2=(4)r7c7-(4)r4c7=(4-6)r4c8=(6)r13c8-(6)r3c7=(hp16)r3c38-(hp27)r2c1/r3c3=(7)r12c2 => r8c2<>7

BTW, storm_norm's move seems invalid for me...
ttt

[storm_norm]

ttt wrote:

BTW, storm_norm's move seems invalid for me...

really?

I am all ears. I would love some insight.
I can only throw it out there so that I may learn why It might be invalid.

[ttt]

ttt wrote:

BTW, storm_norm's move seems invalid for me...

really?
I am all ears. I would love some insight.
I can only throw it out there so that I may learn why It might be invalid.

Code: Select all

*--------------------------------------------------------------------*
 | 3      67     4      |(25)9  (25)79  1      | 279   (5)68   289    |
 | 127    17     8      | 34     6      59     | 2579   125    34     |
 | 5      9      1267   | 8     (2)7    34     | 267    126    34     |
 |----------------------+----------------------+----------------------|
 | 69     8      5      | 1      3      2      | 469    46     7      |
 | 679    2      679    | 459    589    4589   | 569    3      1      |
 | 4      13     13     | 7      59     6      | 8      25     29     |
 |----------------------+----------------------+----------------------|
 | 8      345    23     | 235    1      7      | 24     9      6      |
 | 12679  1567   12679  | 259    4      589    | 3      278    28     |
 | 279    347    2379   | 6      289    389    | 1      2478   5      |
 *--------------------------------------------------------------------*

Your move:
(2)r2c1 = (17)r2c12 - (1)r2c8 = np(25)r26c8 - (5)r1c8 = grp(5-2)r1c45 = (2)r3c5; r3c3 <> 2

Meant: if r1c8<>5 => r1c45<>2 and r3c5=2 right? How can you conclude that?

r1c8 <>5 =>
a/ If r1c4=5 and 2’s at r1c5, r3c5 then can’t conclude r3c5=2
b/ If r1c5=5 and 2’s at r1c4, r3c5 then can’t conclude r3c5=2

ttt

[aran]

Code: Select all

*--------------------------------------------------------------------*
 | 3      67     4      | 259    2579   1      | 279    568    289    |
 | 127    17     8      | 34     6      59     | 2579   125    34     |
 | 5      9      1267   | 8      27     34     | 267    126    34     |
 |----------------------+----------------------+----------------------|
 | 69     8      5      | 1      3      2      | 469    46     7      |
 | 679    2      679    | 459    589    4589   | 569    3      1      |
 | 4      13     13     | 7      59     6      | 8      25     29     |
 |----------------------+----------------------+----------------------|
 | 8      345    23     | 235    1      7      | 24     9      6      |
 | 12679  1567   12679  | 259    4      589    | 3      278    28     |
 | 279    347    2379   | 6      289    389    | 1      2478   5      |
 *--------------------------------------------------------------------*


I didn't find simpler, and some of the moves would be considered nets (but since that's a bad word, I just call them complex chains )
Picking up from position after ttt's excellent first 2 moves (r8c1=1 and <7>r8c2) :
1. deadly rectangle avoidance : 69r45c17
4r4c7=>9r4c1
5r5c7=>9r4c1
hence 7r5c1=9r4c1 : <9>r5c1
2. sashimi finned jellyfish on 7 :
r2589 c1238
fin 7r2c7
a) 7r2c7-5r2c7=5r5c7-(5=489)r5c456-9r5c13=9r4c1
b) 7r2c7-(7=1)r2c2-(17=2)r2c1
hence : -29=7r9c1-7r89c2=7r12c2
=> <7>r3c3
3. simple hidden pair : 59r28c6=8r8c6-(8=2)r8c9-(2=9)r6c9-(9=5)r6c5 : =><5>r5c6
4. complex chain using deadly rectangle avoidance commencing with ttt's xy-wing observation
a) 7r9c2=xy-wing 234-4r7c2=4r7c7-4r4c7=(4-6)r4c8=6r13c8-6r3c7=27r3c57-2r3c3=2r2c1
b) next : deadly rectangle avoidance within this same chain : 27r13c57=> 9r1c57 or 5r1c5
i) 9r1c57-9r1c9=9r6c9-9r4c7=9r4c1
hence - using a) - : -29=7r9c1
ii)
5r1c5-7r1c5=(7-2)r3c5=2r9c5
5r1c5-(5=9)r6c5-(59=8)r5c5-(89=4)r5c6-(4=3)r3c6-3r9c6=3r7c4-(3=2)r7c3-(2=4)r7c7
5r1c5-(5=9)r6c5-(9=2)r6c9-(2=8)r8c9
hence -248=7r9c8
so 7r9c2=7r9c1 or 7r9c2=7r9c8 : =><7>r9c3
5. complex chain
i) 6r8c3=6r8c2-(6=7)r1c2-(7=12)r2c12-(12=5)r2c8-(5=9)r2c6
ii) continuing -(259=7)r2c7-7r3c7=7r3c5
hence -(79=25)r1c45-(2=89)r1c9
iii) 6r8c3=6r8c2-(6=7)r1c2-(7=12)r2c12-(12=5)r2c8-(5=2)r6c8-(2=9)r6c9
hence -89=2r8c9 : =><2>r8c3
6. hidden triple : 125r236c8=6r3c8-6r3c3=6r8c3-(6=5)r8c2-5r8c46=289b8-(89=3)r9c6-(3=4)r3c6-4r5c6 =89r58c6-(89=5)r2c6-5r1c45=5r1c8-(5=2)r6c8 : =><2>r89c8
7. hidden pair : 25r26c8=1r2c8-(1=7)r2c2-(7=6)r1c2-6r3c3=123r367c3 as in 7 etc hence 2r6c8 as above :=><2>r3c8
8. simple chain : 2r7c7=4r7c7-4r4c7=(4-6)r4c7=6r13c8-6r3c7=27r3c57-2r3c3=2r2c1 : =><2>r2c7
9. hidden triple : 123r679=9r9c3-(9=7)r5c3-(79=6)r8c3-(6=5)r8c2-5r8c6=5r2c6-5r1c45=(5-6)r1c8=6r3c8-6r3c7=27r3c57 : <2>r3c3
singles (virtually) to end.

[Steve K]

From the published stuck point, here is a path, not overly nettish.
1) (3=2)r7c3-(2=4)r7c7-(4)r7c2=(4)r9c2 =>r9c2<>3
2) (1=7)r2c2-(7=4)r9c2-r9c8=(4-6)r4c8=r13c8-(6)r3c7=(np27)r3c57-(2)r3c3=(2)r2c1 =>r2c1<>1 one single (lc6)r45c1 => r5c3<>6
3) (5=9)r6c5-(9=2)r6c9-(2=8)r8c9-(8)r8c6=(np59)r28c6 =>r5c6<>5
4) (2=4)r7c7-r9c8=(4-6)r4c8=(6)r13c8-(6)r3c7=(np27)r3c57-(2)r3c3=(2)r2c1 => r2c7<>2
5) (2)r13c7=(2-4)r7c7=(4-5)r7c2=r7c4-r8c6=(5-9)r2c6=r2c7-r1c9=(9-2)r6c9=(2)r6c8 => r2c8<>2 one single
6) (aur27)r13c57=> sis[(2)r9c5,(2)r7c7,(7)r2c7] =>
(2)r9c5.r7c7=(7)r2c7-(7=1)r2c2-(1=5)r2c8-(5=2)r6c8 =>r9c8<>2
7) (5)r2c6=(5-8)r8c6=(ht238)r9c356-(79)r9c3=(nt123)r679c3-(1)r3c3=r2c2-(1=5)r2c8 loop =>
r8c6<>9, r9c56<>9,r8c3<>2,r2c7<>5 => ste

7) alt (aur79)r59c13 => sis[(6)r5c1,(23)r7c9] => (6)r5c1=(nt123)r679c3-(1)r3c3=r2c2-(1=5)r2c8-r2c7=(5)r5c7 =>r5c7<>6 => ste

[Luke]

Well, whaddaya think, Jasper? The good news is that some of the top solvers in the world have offered their ideas. The bad news is we mortals are left to figure out what on earth they're talking about!

01: (1=7)r2c2-(7)r9c2=[XY-wing (234): r9c2, r7c3, r7c7]-(4)r7c2=(4)r7c7-(4)r4c7=(4-6)r4c8=(6)r13c8-(6)r3c7=(hp16-2)r3c38=(2)r2c1 => r2c1<>1, r8c1=1

I find the use of the XY-wing very interesting. Another new idea (for me.) I read it as: 7r9c2 and the XY-wing can't both be false; the 4r7c2 would be the elimination if the XY-wing were true, so they both can't be true => 7r9c2=the XY-wing-4r7c2. Pretty nifty. It seems obvious that if the situation presented itself, nothing would stop one from continuing on into an XY-chain of any length, as long as it came to fruition. After all, an XY-wing is just the shortest possible XY-chain.

4. complex chain using deadly rectangle avoidance commencing with ttt's xy-wing observation
a) 7r9c2=xy-wing 234-4r7c2=4r7c7-4r4c7=(4-6)r4c8=6r13c8-6r3c7=27r3c57-2r3c3=2r2c1
b) next : deadly rectangle avoidance within this same chain : 27r13c57=> 9r1c57 or 5r1c5
i) 9r1c57-9r1c9=9r6c9-9r4c7=9r4c1
hence - using a) - : -29=7r9c1
ii)
5r1c5-7r1c5=(7-2)r3c5=2r9c5
5r1c5-(5=9)r6c5-(59=8)r5c5-(89=4)r5c6-(4=3)r3c6-3r9c6=3r7c4-(3=2)r7c3-(2=4)r7c7
5r1c5-(5=9)r6c5-(9=2)r6c9-(2=8)r8c9
hence -248=7r9c8
so 7r9c2=7r9c1 or 7r9c2=7r9c8 : =><7>r9c3

Thank goodness you noted this was a complex chain. I might have overlooked that fact..... I've got the position as below, with the (27) AUR notated:

Code: Select all

 *-----------------------------------------------------------*
 | 3     67    4     | 259  *2579  1     |*279   568   289   |
 | 27    17    8     | 34    6     59    | 2579  125   34    |
 | 5     9     126   | 8    *27    34    |*267   126   34    |
 |-------------------+-------------------+-------------------|
 | 69    8     5     | 1     3     2     | 469   46    7     |
 | 67    2     79    | 459   589   489   | 569   3     1     |
 | 4     13    13    | 7     59    6     | 8     25    29    |
 |-------------------+-------------------+-------------------|
 | 8     345   23    | 235   1     7     | 24    9     6     |
 | 1     56    2679  | 259   4     589   | 3     278   28    |
 | 279   347   2379  | 6     289   389   | 1     2478  5     |
 *-----------------------------------------------------------*

I know you're not a big net guy, but I recall you mentioning that you'll readily make exceptions when it comes to AURs. Here's what I'm trying to figure out.

1.) The "almost" digits in the AUR are (59) in row 1, and 6r3c7. You address the (59), so why not the 6? Does it have something to do with "=6r13c8?"
2.) The first tentacle (i) establishes that if 9 is the digit that prevents the UR, then =9r4c1. This effectively takes 9r9c1 out of consideration within the chain, and propagation continues =7r9c1. Is that what you meant?
3.) The second tentacle (ii) establishes that if 5 is the digit that prevents the UR, then....holy cow, how did you ever find that? What I think is going on here is the three little chains on 5 combine to see r9c8, leaving only 7r9c8. I'm almost there, but I don't see how the end result of (ii) is linked with 7r9c2, other than they're peers. As usual with new stuff, I'm a little unclear on the concept....

I know that some folks don't like the convoluted chains, but I get a kick out them. There's a new twist around every corner.

[aran]

Luke
What ! Somebody actually examines solutions
There is, it seems to me, a point common to your questions/observations on ttt's xy-wing step and the AUR in that chain of mine.
It's the distinction between assignments/eliminations full-stop (a candidate is definitively placed/eliminated) and assignments/eliminations within chains (a candidate is definitively assigned/eliminated within the chain only)
Call those absolute assignments/elims and relative assignments/elims.
Final hurdle : think of a relative assignment/elim as absolute for the purposes of the chain under consideration only.
Now take those two examples
ttt's chain
(1=7)r2c2-(7)r9c2=XY-wing 234 etc
You IMO shouldn't read it like this

I read it as: 7r9c2 and the XY-wing can't both be false; the 4r7c2 would be the elimination if the XY-wing were true, so they both can't be true => 7r9c2=the XY-wing-4r7c2

but rather as :
7r9c2 has been absolutely eliminated within the chain, hence the XY-wing is absolutely in place within the chain, hence not4r7c2=> 4r7c7 etc.
AUR

The "almost" digits in the AUR are (59) in row 1, and 6r3c7. You address the (59), so why not the 6? Does it have something to do with "=6r13c8?"

6r13c8 having been absolutely assigned within the chain, it follows that 6r3c7 has been absolutely eliminated within the chain.
Hence there is an AUR within the chain which has as absolute within the chain "over" digits 59 (and not 596).

The overall logic was this :
- the chain assigns absolutely within the chain 2r2c1(conclusion of step 4a)
- the chain then backtracks to the AUR with its over digits of 59 so here we have a fork or that word...net
- examination of 9 assigns absolutely within this first fork 9r4c1 (conclusion of step 4bi)
- combined with 2r2c1 this then assigns absolutely within the first fork 7r9c1
- examination of 5 assigns absolutely within the second fork (after some gymnastics) 7r9c8 (conclusion of step 4bii).
So there are now two possible conclusions to the forked chain which began a long time ago at 7r9c2 :
7r9c2=7r9c1 (fork 1) or 7r9c2=7r9c8 (fork 2).
We don't know which hold but whichever holds, the consequences are absolutely dire for 7r9c3.

[Luke]

There is, it seems to me, a point common to your questions/observations on ttt's xy-wing step and the AUR in that chain of mine.
It's the distinction between assignments/eliminations full-stop (a candidate is definitively placed/eliminated) and assignments/eliminations within chains (a candidate is definitively assigned/eliminated within the chain only)

Naw, you (and others) have taught me better than that . While the way I wrote it was obviously confusing, I am absolutely clear on one point: only the end points of the chain matter when it comes to eliminations/placements. As a wise man once said, "One end point must be true."

7r9c2 and the XY-wing can't both be false; the 4r7c2 would be the elimination if the XY-wing were true, so they both can't be true => 7r9c2=the XY-wing-4r7

Here I was figuring out the inferences between the nodes within the confines of the chain only. I didn't intend to make any statement as to what could or couldn't be placed or eliminated. I suppose I shouldn't have used the "therefore" symbol, either.

6r13c8 having been absolutely assigned within the chain, it follows that 6r3c7 has been absolutely eliminated within the chain

Actually, I had figured that out and was looking for affirmation.

examination of 9 assigns absolutely within this first fork 9r4c1 (conclusion of step 4bi)
- combined with 2r2c1 this then assigns absolutely within the first fork 7r9c1

I see that. 4bi allows a continuation of the chain "4a."

examination of 5 assigns absolutely within the second fork (after some gymnastics) 7r9c8 (conclusion of step 4bii).

This I still don't see. 4bi allows the continuation of 4a. How does 4bii do that? Where does 4bii join up with 4a?

I know I'm being dense on this point, but I see the AUR as not part of the chain, but only exerting influence on it from the outside. That's probably where I'm going wrong.

[aran]

examination of 9 assigns absolutely within this first fork 9r4c1 (conclusion of step 4bi)
- combined with 2r2c1 this then assigns absolutely within the first fork 7r9c1

I see that. This is a continuation of the chain "4a."

examination of 5 assigns absolutely within the second fork (after some gymnastics) 7r9c8 (conclusion of step 4bii).

This I still don't see. 4bi allows the continuation of 4a. How does 4bii do that? Where does 4bii join up with 4a?

I know I'm being dense on this point, but I see the AUR as not part of the chain, but only exerting influence on it from the outside. That's probably where I'm going wrong.

Luke
Look at it like this :
the chain arrives at the AUR fork : which involves 59 and not 596 as you agree. Each of which (5/9) constitutes one side of the fork.
Put another way one of those is valid "within the chain".
(nb : there is only one chain, and the forks are only forks in the context of that one chain : 7r9c2=).
Had the chain continued forkless and it did as 4a, 2r2c1 would have been and so was "relatively" assigned.
So it's valid "within the chain" and not merely within a fork and hence valid in conjunction with either fork.
In fact the fork on 9 uses it : 4bi assigns (relatively) 9r4c1. So combining 4a and 4bi ie 2r2c1+9r4c1 =><29>=7r9c1.
That's case 1, or fork 1.
Now return to the AUR and examine the other side of the fork : 5.
Which produces 7r9c8.
PS if this is clear (but it may not be) then it will also be clear that probably I should have stopped originally at the fork rather than backtrack to it after 2r2c1 : a time-saving device...it was meant to be