The New Sudoku Players' Forum

[mona187]

This is a puzzle I dubbed into my program. It verified it and rated it very hard. I have reached a point I cannot go any further without guessing. I would really appreciate it if someone could explain, not just what further reductions are possible, but HOW they arrived at them.

Numbers with asterisks indicate the original puzzle content. All other numbers are my entries. Multiple numbers indicate pencilmarks.

Code: Select all

7    8   9 | 1*   5   2* | 6   4 3*
4*  5*  13 | 89   6  37  | 189 79 2*
12  123 6* | 489 379 347 | 18  57 15
______________________________
12 7* 4    | 6* 123  8   | 5*  23  9
5  9  123  | 37 4*  137  | 23  6  8
6  23  8*  | 5  23   9*  | 4  1*  7
______________________________
8  12 15  | 49 139  1345 | 7* 23 6
9* 6 125  | 37 137  1357 | 23 8* 4*
3*  4  7  | 2* 8    6*   | 19 59 15



I'm not looking for a solution, but coaching at determining how to get there! I tried what I recently read about strong links to eliminate "2" from r7c3. That's about as far as I've advanced. Thanks for any help. I'm still learning, but love the game!

(Could also use some help at getting these grids to line up! )

Mona

[tso]

Code: Select all

+----------------+----------------+----------------+
| 7    8    9    | 1    5    2    | 6    4    3    |
| 4    5    13   | 89   6    37   | 189  79   2    |
| 12   123  6    | 489  379  347  | 18   57   15   |
+----------------+----------------+----------------+
| 12   7    4    | 6    123  8    | 5    23   9    |
| 5    9   -123  |+37   4    137  |+23   6    8    |
| 6    23   8    | 5    23   9    | 4    1    7    |
+----------------+----------------+----------------+
| 8    12   15   | 49   139  1345 | 7    23   6    |
| 9    6    125  |+37  -137 -1357 |+23   8    4    |
| 3    4    7    | 2    8    6    | 19   59   15   |
+----------------+----------------+----------------+


Here is one possible continuation:


1) There are two places in row 3 that can hold a 9 -- both are in box 2 -- therefore, the 9 in box two CANNOT be at r2c4.

However, you can skip step 1 and go directly to the heart of this puzzle, the X-Wing:

2) There are only two places in columns 4 and 7 that can hold a 3, all of which are in rows 5 and 8 (these are marked with '+'. This forms an x-wing -- you can remove the cadidate 3's from the rest of those two rows (marked with '-'. After this, the puzzle will be simple to complete.

To make nice grids, use a simple text editor with a monospaced font such as courier. Some programs and websites will create grids for you.