## Help with unique rectangle/swordfish

Post the puzzle or solving technique that's causing you trouble and someone will help

### Help with unique rectangle/swordfish

I am just getting into the more complex puzzles and am into early Level 3 of the Mensa Absolutely Nasty Sudoku books. I got down to this puzzle and thought I had a swordfish in columns for 9 formed by A3,A8, C3,C7,G7,G8 thereby elminating the 9 at C2. Hopefully I did that correctly. I put this puzzle through Andrew Stuarts Sudoku Solver and it ran right through any swordfish pattern and found a unique rectangle at E7,E9,G7,G9 eliminating the 5's at G7,G9 instead.

*--------------------------------------------------*
| 157 8 159 | 2 4 3 | 6 59 57 |
| 6 2 3 | 5 9 7 | 8 4 1 |
| 457 49 59 | 1 6 8 | 259 3 257 |
|----------------+----------------+----------------|
| 3 5 2 | 7 8 6 | 4 1 9 |
| 8 6 7 | 4 1 9 | 35 2 35 |
| 9 1 4 | 3 5 2 | 7 8 6 |
|----------------+----------------+----------------|
| 15 7 156 | 68 2 4 | 359 59 358 |
| 24 49 69 | 68 3 5 | 1 7 248 |
| 245 3 8 | 9 7 1 | 25 6 245 |
*--------------------------------------------------*

So, because of this, I thought perhaps I am not thinking the swordfish pattern properly. Any help with this will be greatly appreciated.
Thanks
asajar

Posts: 10
Joined: 09 May 2008

Swordfish are 3X3.

3 rows, 3 columns.
wintder

Posts: 297
Joined: 24 April 2007

Here is your layout formatted a little more clearly

Code: Select all
`.------------.------------.----------------.| 157 8   159| 2   4   3  | 6      59   57 || 6   2   3  | 5   9   7  | 8      4    1  || 457 49  59 | 1   6   8  | 259    3    257|:------------+------------+----------------:| 3   5   2  | 7   8   6  | 4      1    9  || 8   6   7  | 4   1   9  | 35a    2    35 || 9   1   4  | 3   5   2  | 7      8    6  |:------------+------------+----------------:| 15  7   156| 68  2   4  | 3a5b9c 5c9  358|| 24  49  69 | 68  3   5  | 1      7    248|| 245 3   8  | 9   7   1  | 2-5    6    245|'------------'------------'------------ ---'`

The 3 Columns 3,7 and 8 have candidate 9 on 4 Rows A,C.G and H (alternatively 1,3,7 and 8),so there is no swordfish here to eliminate a candidate in column 2. If H3 did not possess a candidate 9 then you would have a Swordfish, but a hidden single 9 would pop up first.

I have labelled an XYZ-wing based on the consequences of the 3 choices for r7c7(G7), note the induced 5's labelled a,b and c eliminate the 5 at r9c7(I7). One way of proceeding from here.
Glyn

Posts: 357
Joined: 26 April 2007

Thanks for your help--I now see the problem with this as a swordfish. I will keep working on this. For some reason, I am having trouble grasping that particular technique.
asajar

Posts: 10
Joined: 09 May 2008

### Help with unique rectangle/swordfish

asajar wrote:"...For some reason, I am having trouble grasping that particular technique.

Hi asajar,

A good explanation of the Swordfish technique is described by angusj in the following link... hoping this will help you

http://www.angusj.com/sudoku/hints.php

Cec
Cec

Posts: 1039
Joined: 16 June 2005