The New Sudoku Players' Forum

[JeJ]

When I go to the article in Sudopedia http://www.sudopedia.org/wiki/Empty_Rectangle or the Hodoku Documents http://hodoku.sourceforge.net/en/tech_sdp.php#er , the Empty Rectangle makes perfect sense, but when I play and get stuck and Hodoku gives me the hint of an empty rectangle I can't find it, previous placements confuse me, so could someone please enlight me about this method?

Here's an example of an ER I could not find and still don't see:

Code: Select all

.----------------.------------------.--------------.
| 237  12379  8  | 139   1379  4    | 6    5    37 |
| 37   379    6  | 389   3789  5    | 4    1    2  |
| 5    137    4  | 13    2     6    | 379  379  8  |
:----------------+------------------+--------------:
| 6    278    3  | 1289  189   789  | 279  4    5  |
| 9    5      1  | 23    4     37   | 237  8    6  |
| 4    278    27 | 5     6     3789 | 1    239  37 |
:----------------+------------------+--------------:
| 8    237    27 | 4     5     1    | 237  6    9  |
| 1    6      9  | 7     38    238  | 5    23   4  |
| 237  4      5  | 6     39    239  | 8    237  1  |
'----------------'------------------'--------------'


Hodoku says there is an ER in block 4 and that it connects with the 3,7 pair on c9 but all I seee is the pair.

[daj95376]

There are 4x Empty Rectangles present in this grid. My solver describes them as a line (row/column) combined with a box. The value is indicated in the elimination. The last Empty Rectangle in my list is the one indicated by HoDoKu. The pair listed together do more damage to the puzzle.

Code: Select all

 +-----------------------------------------------------------------------+
 |  237    12379  8      |  139    1379   4      |  6      5      37     |
 |  37     379    6      |  389    3789   5      |  4      1      2      |
 |  5      137    4      |  13     2      6      |  379    379    8      |
 |-----------------------+-----------------------+-----------------------|
 |  6      278    3      |  1289   189    789    |  279    4      5      |
 |  9      5      1      |  23     4      37     |  237    8      6      |
 |  4      278    27     |  5      6      3789   |  1      239    37     |
 |-----------------------+-----------------------+-----------------------|
 |  8      237    27     |  4      5      1      |  237    6      9      |
 |  1      6      9      |  7      38     238    |  5      23     4      |
 |  237    4      5      |  6      39     239    |  8      237    1      |
 +-----------------------------------------------------------------------+
 # 67 eliminations remain

   c3b9  Empty Rectangle                 <> 2    r6c8

   c3b6  Empty Rectangle                 <> 2    r7c7
   c3b6  Empty Rectangle                 <> 7    r7c7

   c9b4  Empty Rectangle                 <> 7    r1c2


[JeJ]

There are 4x Empty Rectangles present in this grid. My solver describes them as a line (row/column) combined with a box. The value is indicated in the elimination. The last Empty Rectangle in my list is the one indicated by HoDoKu. The pair listed together do more damage to the puzzle.

Thanks that shares some light.

May I ask what solver is that you used?

[daj95376]

May I ask what solver is that you used?

It's my solver ... and not suitable for sharing because it's not interactive. It uses command-line directives and output is to a file.

[ronk]

May I ask what solver is that you used?

It's my solver ... and not suitable for sharing because it's not interactive. It uses command-line directives and output is to a file.

JeJ, the Hodoku you are using finds those same four ER eliminations. Just click on the "Find all steps" button and then expand the resultant "Empty Rectangles" list.

daj95376, gsf's solver is command-line too, and lots of people use that.

[JeJ]

Thanks for the replies.

I am understanding this concept more now. I was looking for the rectangle when in fact I should be looking for the column and row candidates are in. This method should be named something like "arrow head" or "L shape" or simply "one colum, one row" or "1r1c" for short and people would get it easier.