The New Sudoku Players' Forum

[deecee]

Stuck on the following hard puzzle from a local paper. Can anyone help please.

--- --- --2
--- --8 -7-
-52 --- 31-

4-8 --7 -2-
--- 2-3 ---
-7- 5-- 6-1

-67 --- 89-
-4- 6-- ---
9-- --- ---


This is as far as I got:

-8- 7-- -62
--- -28 -7-
752 --6 318

4-8 -67 -2-
--- 2-3 7--
27- 5-- 6-1

-67 --2 89-
84- 6-- 2-7
92- 87- 1-6

I have the 49 double in box 2, the 56 double in row 5, and the 49
double in row 1.
What am I missing?

[Hud]

I found 2 x-wings to solve the puzzle. The first was for 4s and the second for 3s. Sorry I can't be more specific.

[udosuk]

I guess you're trying to solve it without pencilmarks... Anyway here is the candidate list:

Code: Select all

 *--------------------------------------------------------------------*
 | 13     8      49     | 7      135    15     | 49     6      2      |
 | 136    39     13469  | 13     2      8      | 459    7      59     |
 | 7      5      2      | 49     49     6      | 3      1      8      |
 |----------------------+----------------------+----------------------|
 | 4      139    8      | 19     6      7      | 59     2      359    |
 | 56     19     56     | 2      1489   3      | 7      48     49     |
 | 2      7      39     | 5      489    49     | 6      348    1      |
 |----------------------+----------------------+----------------------|
 | 135    6      7      | 134    1345   2      | 8      9      34     |
 | 8      4      135    | 6      1359   159    | 2      35     7      |
 | 9      2      35     | 8      7      45     | 1      345    6      |
 *--------------------------------------------------------------------*

After an x-wing from here, only singles are needed for the rest...

[Cec]

Hi deecee,

To help you further along, the X-Wing pattern requires a particular candidate to appear twice and only twice either in two rows and sharing the same two columns in which case the eventual exclusions occur in columns or, using the same logic, where a particular candidate appears twice and only twice in two columns and sharing the same two rows then the exclusions occur in rows.

In your following candidate grid, the 3's form an X-wing pattern in rows 6 and 9, columns 3 and 8 (these cells are marked with an asterisk). Under the above definition, this enables the remaining 3's in columns 3 and 8 to be excluded from the cells marked (A)

Code: Select all

 *--------------------------------------------------------------------*
 | 13     8      49     | 7      135    15     | 49     6      2      |
 | 136    39  (A)13469  | 13     2      8      | 459    7      59     |
 | 7      5      2      | 49     49     6      | 3      1      8      |
 |----------------------+----------------------+----------------------|
 | 4      139    8      | 19     6      7      | 59     2      359    |
 | 56     19     56     | 2      1489   3      | 7      48     49     |
 | 2      7     *39     | 5      489    49     | 6     *348    1      |
 |----------------------+----------------------+----------------------|
 | 135    6      7      | 134    1345   2      | 8      9      34     |
 | 8      4   (A)135    | 6      1359   159    | 2   (A)35     7      |
 | 9      2     *35     | 8      7      45     | 1     *345    6      |
 *--------------------------------------------------------------------*

As already mentioned by udosuk, the puzzle now requires only singles to solve it.

Cec

[deecee]

Thanks guys. I didn't know about x-wings. I'll have another go at the puzzle