The New Sudoku Players' Forum

[John Meyer]

Let me know if you've seen this before but I can't find anything similar and it seems simple enough to be considered a basic strategy. Look at Friday's (6/6/08) Mepham Group sudoku after the basic strategies fail. I have a 5 and 6 in squares A5 and A6 and a 3, 5 and 6 in squares H5 and H6. If the 3 in row H were in H4, H5 and H6 would only have a 5 and 6. Only 5s and 6s in A5, A6, H5 and H6 would lead to an ambiguous situation that would not produce a unique solution. Since the sudoku does have a unique solution H5 or H6 must be a 3. This means that H4 cannot be a 3. Now the sudoku can be solved to completion. I have several more examples with graphics on a Word file I would be glad to send anyone interested. My email address is jmeyer2@knology.net. If you have an archive you might also want to check out The Mepham Group's 1/11/08, 2/29/08, 3/28/08 and 4/25/08 before looking at my examples. 1/11/08 doesn't seem to lead to a solution but is still interesting.
John Meyer

[Glyn]

The Mepham group produce a number of different daily puzzles. After a little detective work it seems that you were refering to the Los Angeles Times puzzle 0f 6/6/08 ,which is:

Code: Select all

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

The point you are refering to is probably something like:

Code: Select all

---------------.----------------.---------------.
| 3    9    7   | 8    *56  *56  | 2    1    4   |
| 4    6    1   | 23    39   29  | 7    8    5   |
| 28   28   5   | 4     7    1   | 9    6    3   |
:---------------+----------------+---------------:
| 17   147  2   | 36    8    346 | 5    9    16  |
| 5    3    6   | 9     1    7   | 4    2    8   |
| 18   148  9   | 56    2    456 | 3    7    16  |
:---------------+----------------+---------------:
| 6    27   3   | 1     4    29  | 8    5    79  |
| 9    17   8   |-3567 *356 *356 | 16   4    2   |
| 127  5    4   | 267   69   8   | 16   3    79  |
'---------------'----------------'---------------'

The elimination of the 3 at r8c4 is fairly commonly called Unique Rectangle Type 2-a or Unique Side.
For more on these have a look here, Standardizing the Uniqueness descriptions...

[John Meyer]

Thanks Glyn

The unique rectangles are indeed what I'm talking about. I've posted some examples of loops, triples and quads on (I think) the link you supplied above.