The New Sudoku Players' Forum

[heathcliff]

I've recently become addicted to Sudoku, I downloaded an app called Sudoku on my ipad and can finish the hard levels within 6 or 7 minutes. Recently I've started attempting the extreme but I can't seem to finish them without guessing between one of the possibilities to get me going again.

I've thought about all the possibilities in this one and can't seem to figure out where to go next. I've attached the screenshot of my game. Any help is GREATLY appreciated.

[Pat]

you could try posting the puzzle as text
( just the known cells )

probably needs "forcing chains"---

[JasonLion]

Remote pairs will allow you to make progress. I also see a unique rectangle and another remote pair further on.

[heathcliff]

by remote pairs you mean the 2 possibilities such as 29 and 29?

I have used something like that ( not sure what it's called) but if I had 3 unknowns in a box and the possibilities were 29 29 and 279, logic would dictate that the box with possibilities 279 must be 7.

[JasonLion]

It sounds like you are talking about regular pairs and triples. Remote pairs are different, though slightly related. For more info on remote pairs see here or here (or many other places).

[heathcliff]

Thanks for the links, but I'm still stumped (I checked other sites about remote pairs too). In the case of remote pairs, say 29 in my example,I know I'm supposed to have an even number but I have an uneven number of 29's. Also does it matter where I start?

In the case of 79's I'm also unsure where I would start or how the intersection of the ends would eliminate a possibility.

Sorry if I'm posting stupid questions but I would like to learn as much as I can.

[JasonLion]

It doesn't matter if there are more then four 29's on the board, you can pick any four (or six, or eight) of them to use for a chain. It doesn't matter where you start, or which of them you use and which you don't use, as long as you can form a chain of an appropriate length that follows the rules and provides at least one elimination. There is a fairly obvious elimination from a remote pair of 29's.

[daj95376]

Code: Select all

 *---------------------------------------------------------------------*
 | 79     5      8      | 279    279    6      |  1      3      4      |
 | 3      1      79     | 579    5789   4      |  259    6      289    |
 | 4      6      2      | 1      3      589    |  59     7      89     |
 |----------------------+----------------------+-----------------------|
 | 1      4      5      | 3      2789   78-29  |  6     a29     279    |
 | 79     2      6      | 4      579    579    |  3      8      1      |
 | 8      3      79     | 6      279    1      |  4      5      279    |
 |----------------------+----------------------+-----------------------|
 | 5      7      4      | 8      6     d29     | c29     1      3      |
 | 2      9      3      | 57     1      57     |  8      4      6      |
 | 6      8      1      | 29     4      3      |  7     b29     5      |
 *---------------------------------------------------------------------*

 RP:   a           b           c           d        =>  r4c6<>29   specifically ...

     (2=9)r4c8 - (9=2)r9c8 - (2=9)r7c7 - (9=2)r7c6  =>  r4c6<>2
     (9=2)r4c8 - (2=9)r9c8 - (9=2)r7c7 - (2=9)r7c6  =>  r4c6<>9


Code: Select all

 after the dust clears
 *-----------------------------------------------------------*
 | 79    5     8     | 2    p79    6     | 1     3     4     |
 | 3     1     79    | 57    5789  4     | 2     6     89    |
 | 4     6     2     | 1     3    v89    | 5     7     89    |
 |-------------------+-------------------+-------------------|
 | 1     4     5     | 3     28-7 p78    | 6     9     27    |
 | 79    2     6     | 4     59-7  579   | 3     8     1     |
 | 8     3     79    | 6     29-7  1     | 4     5     27    |
 |-------------------+-------------------+-------------------|
 | 5     7     4     | 8     6     2     | 9     1     3     |
 | 2     9     3     | 57    1     57    | 8     4     6     |
 | 6     8     1     | 9     4     3     | 7     2     5     |
 *-----------------------------------------------------------*

                    v    p    p

 <89+7>  XY-Wing  r3c6/r1c5+r4c6         <> 7    r456c5

   c6b5  Locked Candidate 1              <> 7    r8c6


Code: Select all

 after the dust clears
 *--------------------------------------------------*
 | 79   5    8    | 2    79   6    | 1    3    4    |
 | 3    1    79   | 5    78=9 4    | 2    6    89   |
 | 4    6    2    | 1    3    89   | 5    7    89   |
 |----------------+----------------+----------------|
 | 1    4    5    | 3    28   78   | 6    9    27   |
 | 79   2    6    | 4    5    79   | 3    8    1    |
 | 8    3    79   | 6    29   1    | 4    5    27   |
 |----------------+----------------+----------------|
 | 5    7    4    | 8    6    2    | 9    1    3    |
 | 2    9    3    | 7    1    5    | 8    4    6    |
 | 6    8    1    | 9    4    3    | 7    2    5    |
 *--------------------------------------------------*

         BUG+1                           =  9    r2c5


[Pat]

Code: Select all


 . 5 8 | . . 6 | 1 3 4
 3 1 . | . . 4 | . 6 .
 4 6 2 | 1 3 . | . 7 .
-------+-------+------
 1 4 5 | 3 . . | 6 . .
 . 2 6 | 4 . . | 3 8 1
 8 3 . | 6 . 1 | 4 5 .
-------+-------+------
 5 7 4 | 8 6 . | . 1 3
 2 9 3 | . 1 . | 8 4 6
 6 8 1 | . 4 3 | 7 . 5



daj95376, thanks for posting the text version

heathcliff, i didn't solve this myself, but with help from software -- i now know that 2 moves will solve this puzzle

each move is a "turbot"
( a type of "forcing chains",
and can also be considered a "finned" X-wing )

first move: one of these --

• (2) r7c8\r4b9 with "fin" r7c6
  
• (2) r7c8\c6b9 with "fin" r4c8
( or "turbot" )
--> r4c6 not 2,

solves c6 2 ...



Code: Select all


 . 5 8 | 2 . 6 | 1 3 4
 3 1 . | . . 4 | 2 6 .
 4 6 2 | 1 3 . | 5 7 .
-------+-------+------
 1 4 5 | 3 . . | 6 9 .
 . 2 6 | 4 . . | 3 8 1
 8 3 . | 6 . 1 | 4 5 .
-------+-------+------
 5 7 4 | 8 6 2 | 9 1 3
 2 9 3 | . 1 . | 8 4 6
 6 8 1 | 9 4 3 | 7 2 5




2nd move:
(9) c16\r15 with "fin" r3c6
( or "turbot" )
--> r1c5 not 9