The New Sudoku Players' Forum

[retired_engineer]

Hi:

Am stuck on this one. I'll put it down and come back to it, but no luck. Even tried starting from the beginning, but got to the same place. I have the sudoku.com program, but it has no more hints. I guess it must require advanced techniques?

*-----------*
|173|...|...|
|25.|...|641|
|46.|125|..3|
|---+---+---|
|.82|...|..9|
|9.5|871|...|
|6..|...|5.8|
|---+---+---|
|82.|436|...|
|594|...|...|
|..6|...|284|
*-----------*


*-----------*
|173|...|...|
|25.|...|641|
|46.|125|..3|
|---+---+---|
|.82|...|..9|
|9.5|871|...|
|6..|...|5.8|
|---+---+---|
|82.|436|...|
|594|...|...|
|..6|...|284|
*-----------*


*-----------------------------------------------------------*
| 1 7 3 | 69 4689 489 | 89 25 25 |
| 2 5 89 | 37 89 37 | 6 4 1 |
| 4 6 89 | 1 2 5 | 789 79 3 |
|-------------------+-------------------+-------------------|
| 37 8 2 | 56 56 34 | 1347 137 9 |
| 9 34 5 | 8 7 1 | 34 26 26 |
| 6 134 17 | 239 49 2349 | 5 37 8 |
|-------------------+-------------------+-------------------|
| 8 2 17 | 4 3 6 | 19 159 57 |
| 5 9 4 | 27 18 278 | 13 136 67 |
| 37 13 6 | 579 159 79 | 2 8 4 |
*-----------------------------------------------------------*

Just did a 'paste' so not sure why the 1st 3 boxes above came out the way they did. I was thinking only the bottom grid would appear. To you 'regular' players on this forum, is this a helpful and/or the usual format in which to present my problem?

Thanks, Doug

[udosuk]

Surround your grids with [code] and [/code] tags:

Code: Select all

 *-----------*
 |173|...|...|
 |25.|...|641|
 |46.|125|..3|
 |---+---+---|
 |.82|...|..9|
 |9.5|871|...|
 |6..|...|5.8|
 |---+---+---|
 |82.|436|...|
 |594|...|...|
 |..6|...|284|
 *-----------*

 *-----------*
 |173|...|...|
 |25.|...|641|
 |46.|125|..3|
 |---+---+---|
 |.82|...|..9|
 |9.5|871|...|
 |6..|...|5.8|
 |---+---+---|
 |82.|436|...|
 |594|...|...|
 |..6|...|284|
 *-----------*
 
 *-----------------------------------------------------------*
 | 1     7     3     | 69    4689  489   | 89    25    25    |
 | 2     5     89    | 37    89    37    | 6     4     1     |
 | 4     6     89    | 1     2     5     | 789   79    3     |
 |-------------------+-------------------+-------------------|
 | 37    8     2     | 56    56    34    | 1347  137   9     |
 | 9     34    5     | 8     7     1     | 34    26    26    |
 | 6     134   17    | 239   49    2349  | 5     37    8     |
 |-------------------+-------------------+-------------------|
 | 8     2     17    | 4     3     6     | 19    159   57    |
 | 5     9     4     | 27    18    278   | 13    136   67    |
 | 37    13    6     | 579   159   79    | 2     8     4     |
 *-----------------------------------------------------------*

You're right it requires advance techniques. My method is to use a nishio (check out column 5, if r8c5=8 then you must have both r1c4 and r1c5 having 6)... I hope someone could show a less T&E-feel technique...

[daj95376]

retired_engineer, There are two nightmare XY-Chains that'll solve your puzzle. Previously, the longest XY-Chain I'd ever encountered was of n=9 cells.

Code: Select all

Puzzle:

173......25....64146.125..3.82.....99.5871...6.....5.882.436...594........6...284

r2      -  89    Naked  Pair
r5      -  34    Naked  Pair
    b6  -  26    Naked  Pair
    b3  -  789   Naked  Triple
r4      -  1347  Naked  Quad
    b4  -  1     Locked Candidate (1)
  c9    -  7     Locked Candidate (2)
r8c6    <> 7     XY-Chain on [r2c6]   (n=15)
r1c6    <> 8     XY-Chain on [r1c7]   (n=14)
                Naked/Hidden Singles to finish

<73><34><49><98><81><13><34><43><37><71><17><75><52><26><67>
<89><91>            <13><34><43><37><71><17><75><52><26><67><72><28>

-OR-

You can use Elimination-by-Contradiction to replace the two XY-Chains.
(Details not included, but it should be simple to duplicate if you stay in columns 4/5/6.)

r1c4    =  6     [r1c4]=9 => [r9]=INVALID


[tso]

Code: Select all

 *-----------------------------------------------------------*
 | 1     7     3     | 69    4689  489   | 89    25    25    |
 | 2     5     89    | 37    89    37    | 6     4     1     |
 | 4     6     89    | 1     2     5     | 789   79    3     |
 |-------------------+-------------------+-------------------|
 |[37]   8     2     | 56    56    34    | 134x7 13x7  9     |
 | 9    [34]   5     | 8     7     1     |[34]   26    26    |
 | 6     134   1x7   | 239   49    2349  | 5    [37]   8     |
 |-------------------+-------------------+-------------------|
 | 8     2     17    | 4     3     6     | 19    159   57    |
 | 5     9     4     | 27    18    278   | 13    136   67    |
 | 37    13    6     | 579   159   79    | 2     8     4     |
 *-----------------------------------------------------------*

This is a good one. A simple 5-cell xy forcing chain reduces this to singles.

Examine the four cells in [brackets]. At least one of the two [37] cells must be 7 -- this excludes the three 7s marked with 'x'.

Interesting pattern -- a less powerful variant of "remote pairs".

[retired_engineer]

thanks everybody.

I've got to look up the nishio method and find out about that.

I'm going to print these replies out and really study them. I guess it's time for me to move to a higher level of puzzle solving.

onward and upward - to enlightenment ;-)

Doug