The New Sudoku Players' Forum

[Snowman9000]

From Chicago Tribune 26 March 2017. By The Mephan Group. Rated 3 of 4 difficulty.
I am stuck. Looking for X Wing, XY Wing, Swordfish.... Can you give me one hint? Thanks!

[JasonLion]

I see a Unique Rectangle.

[Leren]

6...892..92.146.....4.2396..7..9542...5.3.7...98..7.53.429..3......52.....9.7...2

I see two simple solutions. The first one is the Unique Rectangle mentioned by Jason : The UR is in r56c14 (cells marked *) and shows that r5c4 can't be 2 or 4.

Code: Select all

*-----------------------------------------------------------------------*
| 6      135    137     | 57     8      9       | 2      1347   147     |
| 9      2      37      | 1      4      6       | 58     378    578     |
| 1578   158    4       | 57     2      3       | 9      6      17      |
|-----------------------+-----------------------+-----------------------|
| 13     7      136     | 68     9      5       | 4      2      168     |
|*24     16     5       |*68-24  3      148     | 7      189    1689    |
|*24     9      8       |*24     16     7       | 16     5      3       |
|-----------------------+-----------------------+-----------------------|
| 1578   4      2       | 9      16     18      | 3      178    15678   |
| 1378   1368   1367    | 3468   5      2       | 168    14789  146789  |
| 1358   13568  9       | 3468   7      148     | 1568   148    2       |
*-----------------------------------------------------------------------*

The second is a Skyscraper, in the cells marked a-b-c-d below. This shows that at least one of cells a or d must be 6, so 6 can be removed from r45c9 and r89c7.

Code: Select all

*-----------------------------------------------------------------------*
| 6      135    137     | 57     8      9       | 2      1347   147     |
| 9      2      37      | 1      4      6       | 58     378    578     |
| 1578   158    4       | 57     2      3       | 9      6      17      |
|-----------------------+-----------------------+-----------------------|
| 13     7      136     | 68     9      5       | 4      2      18-6    |
| 24     16     5       | 2468   3      148     | 7      189    189-6   |
| 24     9      8       | 24    b16     7       |a16     5      3       |
|-----------------------+-----------------------+-----------------------|
| 1578   4      2       | 9     c16     18      | 3      178   d15678   |
| 1378   1368   1367    | 3468   5      2       | 18-6   14789  146789  |
| 1358   13568  9       | 3468   7      148     | 158-6  148    2       |
*-----------------------------------------------------------------------*

In both cases the puzzle solves with singles after each of the moves. If you need help with any of this let me know and I'll explain further.

Leren

[Snowman9000]

Thank you both. I used the unique rectangle you both spotted. I had used unique rectangle only once before, and did not understand until now exactly why the odd cell can't contain the two candidates. This will help me going forward.

I did not try to learn the skyscraper at this time. I need to digest these one at a time, I think.