The New Sudoku Players' Forum

[stumble]

Original AU12-25-07Tough
Usually I stay away from puzzles this hard, but Christmas day I seemed to be either smarter or doing easy ones. So I tried this one:

Code: Select all

.------------------------.------------------------.------------------------.
| 3       1267    12456  | 2467    1247    1467   | 8       9       257    |
| 14567   1267    12456  | 9       12478   14678  | 123457  23457   2357   |
| 147     8       1249   | 2347    5       147    | 12347   2347    6      |
:------------------------+------------------------+------------------------:
| 9       4       2356   | 1       278     578    | 23567   23578   23578  |
| 8       1237    1235   | 2457    6       457    | 2357    2357    9      |
| 567     267     256    | 2578    2789    3      | 2567    1       4      |
:------------------------+------------------------+------------------------:
| 2       19      1489   | 4578    3       145789 | 4579    6       578    |
| 146     1369    134689 | 45678   14789   2      | 34579   34578   3578   |
| 46      5       7      | 468     489     4689   | 2349    2348    1      |
'------------------------'------------------------'------------------------'


this is as far as I can get. Ought to be some hiddens in there, but I can’t see ‘em.

Code: Select all

.---------------------.---------------------.---------------------.
| 3      127    1245  | 47     124    6     | 8      9      57    |
| 14567  1267   12456 | 9      124    8     | 1457   457    3     |
| 147    8      9     | 3      5      17    | 1247   247    6     |
:---------------------+---------------------+---------------------:
| 9      4      36    | 1      7      5     | 36     8      2     |
| 8      137    135   | 2      6      4     | 357    357    9     |
| 567    267    256   | 8      9      3     | 567    1      4     |
:---------------------+---------------------+---------------------:
| 2      19     148   | 457    3      17    | 4579   6      578   |
| 146    1369   13468 | 4567   14     2     | 4579   457    578   |
| 46     5      7     | 46     8      9     | 23     23     1     |
'---------------------'---------------------'---------------------


[Pat]

Original AU12-25-07Tough
Usually I stay away from puzzles this hard, but Christmas day I seemed to be either smarter or doing easy ones. So I tried this one:

Code: Select all

.------------------------.------------------------.------------------------.
| 3       1267    12456  | 2467    1247    1467   | 8       9       257    |
| 14567   1267    12456  | 9       12478   14678  | 123457  23457   2357   |
| 147     8       1249   | 2347    5       147    | 12347   2347    6      |
:------------------------+------------------------+------------------------:
| 9       4       2356   | 1       278     578    | 23567   23578   23578  |
| 8       1237    1235   | 2457    6       457    | 2357    2357    9      |
| 567     267     256    | 2578    2789    3      | 2567    1       4      |
:------------------------+------------------------+------------------------:
| 2       19      1489   | 4578    3       145789 | 4579    6       578    |
| 146     1369    134689 | 45678   14789   2      | 34579   34578   3578   |
| 46      5       7      | 468     489     4689   | 2349    2348    1      |
'------------------------'------------------------'------------------------'


this is as far as I can get. Ought to be some hiddens in there, but I can’t see ‘em.

Code: Select all

.---------------------.---------------------.---------------------.
| 3      127    1245  | 47     124    6     | 8      9      57    |
| 14567  1267   12456 | 9      124    8     | 1457   457    3     |
| 147    8      9     | 3      5      17    | 1247   247    6     |
:---------------------+---------------------+---------------------:
| 9      4      36    | 1      7      5     | 36     8      2     |
| 8      137    135   | 2      6      4     | 357    357    9     |
| 567    267    256   | 8      9      3     | 567    1      4     |
:---------------------+---------------------+---------------------:
| 2      19     148   | 457    3      17    | 4579   6      578   |
| 146    1369   13468 | 4567   14     2     | 4579   457    578   |
| 46     5      7     | 46     8      9     | 23     23     1     |
'---------------------'---------------------'---------------------


well it's too tough for me -- but here's what SuDoku Explainer suggests --

Nishio Forcing Chains

With this solving technique, we will prove the two following assertions:

If R3C6 contains the value 1, then R2C1 must contain the value 1
If R3C6 contains the value 1, then R2C1 cannot contain the value 1

Because the same assumption yields to contradictory results, we can conclude that the assumption is false, that is, R3C6 cannot contain the value 1.

Each assertion is proved by a different chain of simple rules. The chains are Nishio chains: they only involve a single value (like Forcing X-Chains), but the conclusions of multiple sub-chains must be combined in some cases.

The details of each chain are given below.

Chain 1: If R3C6 contains the value 1, then R2C1 cannot contain the value 1:

(1) If R3C6 contains the value 1, then R2C5 cannot contain the value 1 (the value can occur only once in the block)
(2) If R3C6 contains the value 1 (initial assumption), then R1C5 cannot contain the value 1 (the value can occur only once in the block)
(3) If R1C5 does not contain the value 1 and R2C5 does not contain the value 1 (1), then R8C5 must contain the value 1 (only remaining possible position in the column)
(4) If R8C5 contains the value 1, then R8C1 cannot contain the value 1 (the value can occur only once in the row)
(5) If R3C6 contains the value 1 (initial assumption), then R3C1 cannot contain the value 1 (the value can occur only once in the row)
(6) If R3C1 does not contain the value 1 and R8C1 does not contain the value 1 (4), then R2C1 must contain the value 1 (only remaining possible position in the column)

Chain 2: If R2C1 must contain the value 1, then R2C1 cannot contain the value 1:

(1) If R3C6 contains the value 1, then R3C7 cannot contain the value 1 (the value can occur only once in the row)
(2) If R3C7 does not contain the value 1, then R2C7 must contain the value 1 (only remaining possible position in the block)
(3) If R2C7 contains the value 1, then R2C1 cannot contain the value 1 (the value can occur only once in the row)

[tarek]

not easy....

one proposed method

Code: Select all

*-----------------------------------------------------------------*
| 3     %127   %1245  | 47    #124    6     | 8      9      57    |
|*14567  1267   12456 | 9     *124    8     |*1457   457    3     |
|*147    8      9     | 3      5     -17    |*1247   247    6     |
|---------------------+---------------------+---------------------|
| 9      4      36    | 1      7      5     | 36     8      2     |
| 8     %137   %135   | 2      6      4     | 357    357    9     |
| 567    267    256   | 8      9      3     | 567    1      4     |
|---------------------+---------------------+---------------------|
| 2     %19    %148   | 457    3     %17    | 4579   6      578   |
|*146    1369   13468 | 4567  *14     2     | 4579   457    578   |
| 46     5      7     | 46     8      9     | 23     23     1     |
*-----------------------------------------------------------------*
Eliminating 1 From r3c6 (Finned Swordfish(*) in r238c157 with 1 fin(#) in Box 2, or by constructing the Finned Swordfish(%) in r157c236 with 1 fin(#) in Box 2)

tarek

[Pat]

beautiful, tarek -- with all the talk about finned fish, i still never seem to find them

[stumble]

Well, at least you guys said my question was hard this time. But 16 MINUTES? You still bruised my tender ego - I been two days on the thing.

[tarek]

beautiful, tarek -- with all the talk about finned fish, i still never seem to find them

Thanx, this was easier than most because It worked from the 1st attempt.
r3c6 was the 1st sell I attempted to attack because it was the 1st that caught my eye (next would have been r1c9)...& i started with the 1s.

The finned swordfish r238c157 is the one I constructed as it looks like a swordfish without the fin (so it is not a sashimi)

I usually give up if my attack on bivalue cells is not fruitful

tarek

[Pat]

Well, at least you guys said my question was hard this time.

But 16 MINUTES? You still bruised my tender ego - I been two days on the thing.

I admitted it was too tough for me.

And therefore, just gave up and turned quickly to the software for help.

[tarek]

I had too much practice with finned basic swordfish from posting so many puzzles in the hardest thread that had it as a 1st move.

I manually find it eventually but I find one quickly <20% of the time

There was a finned mutant x-wing earlier today in a puzzle (I failed to spot that )

tarek

[stumble]

I had too much practice with finned basic swordfish from posting so many puzzles in the hardest thread that had it as a 1st move.

I manually find it eventually but I find one quickly <20% of the time

There was a finned mutant x-wing earlier today in a puzzle (I failed to spot that )

tarek

I don't think I'll even attempt to read up on finned mutants. At least not yet. Takes me forever to arrange an Alternating Reference Chain (my favorite tool). BTW thanks for that SuDoku Explainer link, Pat. I didn't have that. Yet another resource when all else fails.

[daj95376]

this is as far as I can get. Ought to be some hiddens in there, but I can’t see ‘em.

Code: Select all

.---------------------.---------------------.---------------------.
| 3      127    1245  | 47     124    6     | 8      9      57    |
| 14567  1267   12456 | 9      124    8     | 1457   457    3     |
| 147    8      9     | 3      5      17    | 1247   247    6     |
:---------------------+---------------------+---------------------:
| 9      4      36    | 1      7      5     | 36     8      2     |
| 8      137    135   | 2      6      4     | 357    357    9     |
| 567    267    256   | 8      9      3     | 567    1      4     |
:---------------------+---------------------+---------------------:
| 2      19     148   | 457    3      17    | 4579   6      578   |
| 146    1369   13468 | 4567   14     2     | 4579   457    578   |
| 46     5      7     | 46     8      9     | 23     23     1     |
'---------------------'---------------------'---------------------


Aaaah, one of my favorites. A cell with three strong links leading to a nice or else condition.

Code: Select all

[r7c6]=1 or else [r3c6],[r7c23],[r8c5]=1


There are four finned Swordfish that eliminate various combinations of the or else cells. Hovever, sometimes a single-digit contradiction chain is nice for a diversion.

Code: Select all

(1) [r8c5]-[r1c5]=[r1c23]-[r23c1]=[r8c1]-[r8c5] contradiction!


[pmsmith]

Hi Stumble,
I am having trouble getting to your original stuck position. I have

Code: Select all

*-----------------------------------------------------------------------------------------*
| 3        127      1245      | 247      1247     6         | 8        9        257       |
| 14567    1267     12456     | 9        1247     8         | 123457   23457    2357      |
| 147      8        9         | 3        5        147       | 1247     247      6         |
|-----------------------------+-----------------------------+-----------------------------|
| 9        4        2356      | 1        27       57        | 23567    23578    23578     |
| 8        1237     1235      | 2457     6        457       | 2357     2357     9         |
| 567      267      256       | 8        9        3         | 2567     1        4         |
|-----------------------------+-----------------------------+-----------------------------|
| 2        19       148       | 457      3        1457      | 4579     6        578       |
| 146      1369     13468     | 4567     147      2         | 4579     4578     578       |
| 46       5        7         | 46       8        9         | 23       23       1         |
*-----------------------------------------------------------------------------------------*



What diid you do to move along to your initial stuck position?

Thanks
Peter

[daj95376]

What diid you do to move along to your initial stuck position?

If you don't mind an answer from someone other than Stumble, you're missing a Locked Candidate (2) in [r3b3] and singles that follow.

[stumble]

What diid you do to move along to your initial stuck position?

If you don't mind an answer from someone other than Stumble, you're missing a Locked Candidate (2) in [r3b3] and singles that follow.

Thanks daj95376, I would have had to reinvent the wheel to duplicate my efforts.

[pmsmith]

Thank you daj95376.

By-the-way the java tool that another member suggested Sudoku Explainer (http://diuf.unifr.ch/people/juillera/Sudoku/Sudoku.html) is a really excellent teaching resource!

Peter