## Do I have to guess now? I hate guessing :)

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

### Do I have to guess now? I hate guessing :)

I have reached the following point in a Sudoku that has been driving me (and a few other folks) crazy. None of us can figure out how to logically determine the next step without guessing and checking to see if it fails.

Code: Select all
` . 1 . | 6 . 2 | . 8 .  6 . . | . . 3 | . 1 5  4 . 3 | . 1 . | . . 6 -------+-------+------  8 . . | . . 7 | . . 4  . . 1 | . 2 4 | 6 7 8  7 . . | 9 8 . | . . 2 -------+-------+------  2 . . | . 3 . | 8 . 7  1 6 8 | 2 7 . | . 4 .  3 7 . | 4 . 8 | . . 1 `

Please help us so that we can get on with our lives.

Cheers and Happy New Years!
robboyer

Posts: 2
Joined: 01 January 2006

You have an X-wing of 3s on r1c7, r1c9, r8c7, r8c9, which allows you to remove the 3s on r4c7 and r6c7
jphamel

Posts: 17
Joined: 27 December 2005

Where is the puzzle from as it requires something like a chain to solve ( out of my current depth )

Did find 2 X-Wings in 3 and managed to place 3 in R5C4, but this is not much help.

ps What is the puzzle rated
Crazy Girl

Posts: 189
Joined: 08 November 2005

The candidate grid from your position:

Code: Select all
`  59    1     579   | 6     459   2     | 3479     8     39      6     289   279   | 78    49    3     | 2479     1     5       4     2589  3     | 578   1     59    | 279      29    6      -------------------+-------------------+-----------------------  8     2359  2569  | 135   56    7     | 1359     359   4       59    359   1     | 35    2     4     | 6        7     8       7     345   456   | 9     8     156   | 135      35    2      -------------------+-------------------+----------------------  2     459   459   | 15    3     1569  | 8        569   7       1     6     8     | 2     7     59    | 359      4     39      3     7     59    | 4     569   8     | 259      2569  1   `

These four moves that can be made in any order:

-- The {3s} in column 8 are locked in box 6, eliminating 3s from r46c7.
-- The (9s) in box 6 are locked in row 4, elliminating 9s from r4c23.
-- The naked pair [59][59] in the 6th column eliminates the 5s and 9s from r67c6.
-- The naked triple <459><49><59> in box 2 eliminate the 5 from r3c4.

Code: Select all
`  59    1     579   | 6    <459>  2     | 3479     8      39      6     289   279   | 78   <49>   3     | 2479     1      5       4     2589  3     | 578   1   <[59]>  | 279      29     6      -------------------+-------------------+----------------------  8     2359  2569  | 135   56    7     | 135(9)  {3}5(9)  4       59    359   1     | 35    2     4     | 6        7       8       7     345   456   | 9     8     156   | 135     {3}5     2      -------------------+-------------------+----------------------  2     459   459   | 15    3     1569  | 8        569     7       1     6     8     | 2     7    [59]   | 359      4       39      3     7     59    | 4     569   8     | 259      2569    1     `

Updating the candidate grid:
Code: Select all
`  59    1     579   | 6     459   2     | 3479  8     39      6     289   279   | 78    49    3     | 2479  1     5       4     2589  3     | 78    1     59    | 279   29    6      -------------------+-------------------+-------------------  8     235   256   | 135   56    7     | 159   359   4       59    359   1     | 35    2     4     | 6     7     8       7     345   456   | 9     8     16    | 15    35    2      -------------------+-------------------+-------------------  2     459   459   | 15    3     16    | 8     569   7       1     6     8     | 2     7     59    | 359   4     39      3     7     59    | 4     569   8     | 259   2569  1     `

Advanced Coloring 9s excludes 9 from r1c5, r3c7 and r3c8:
Code: Select all
`  59    1     579   | 6     x459  2     | 3479  8    d39      6     289   279   | 78    49    3     | 2479  1     5       4     2589  3     | 78    1    a59    |x279  x29    6      -------------------+-------------------+-------------------  8     235   256   | 135   56    7     | 159   359   4       59    359   1     | 35    2     4     | 6     7     8       7     345   456   | 9     8     16    | 15    35    2      -------------------+-------------------+-------------------  2     459   459   | 15    3     16    | 8     569   7       1     6     8     | 2     7    b59    | 359   4    c39      3     7     59    | 4    a569   8     | 259   2569  1    `

After this, there are many singles -- then you'll hit another similar log jam from which there will be more than one way to go -- either coloring or forcing chains, etc.
tso

Posts: 798
Joined: 22 June 2005

Thanks, tso! I was stuck on the part that you used "advanced coloring" for. It is an interesting concept, but I don't think I would have known where to look, even with this new tool, if someone hadn't pointed it out to me. In a way, it really doesn't seem all that different from taking a guess and proving that it's wrong, but I suppose it does keep you on one track.
BTW, Crazy Girl, I'm not sure the source of this puzzle (I only got a copy of it)... I do know it is apparently a 6 (out of 6) star puzzle.
Thanks again.
robboyer

Posts: 2
Joined: 01 January 2006

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