The New Sudoku Players' Forum

[eniacap]

Slightly off topic but further to the swordfish, what about this:-

XX.|..X|
. X.|..X|
XX.|... |

This would seem to fit the criterion, but when I start at the top left, going anti-clockwise, marking alternate + & - to complete the loop, I finish with 2 pluses top left.
This is impossible so should the second X in the top row be redundant?

[Glyn]

eniacap In your last example the pattern of X's restricted to 3 columns and 3 rows is also restricted to 2 boxes, so it is not a Swordfish.

There are 7 possible arrangements of the X's in the limited area of the grid none of which indicate an elimination.

In contrast the Times Swordfish is spread over 6 boxes.

[eniacap]

Sorry I left out a line thinking it irrelevant to the problem Doh!!

The diagram should be:-

|X X . |. . X |
| . . . | . . . |
| . X . | . . X|
|X X . | . . . |

[Glyn]

eniacap Your latest grid covering rows 1-4 and columns 1-6 has X's restricted to 3 rows, 3 columns and 3 boxes.

These 3 arrangements would be valid

Code: Select all

|a  b . |. . c  |
|.  . . |. . .  |
|.  c . |. . ab |
|bc a . |. . .  |

As a whole it is the residual pattern that would be left after clearing either the more familiar row/column Swordfish or the more advanced concept of row/box or column/box Swordfish.

[eniacap]

Thanks Glyn.
When under the illusion that a swordfish had 2 candidates in each of 3 columns/rows, it was simple to check as described above by forming a closed loop with alternating false/true. Is there a simple way of checking one has a swordfish when there are columns/rows containing 3 candidates?

[Glyn]

eniacap The most complete Swordfish is 9 candidate positions 3 per row/column. Up to 3 candidates can be missing as long as there are at least 2 per row/column. The case you have been thinking of is the sparsest form of the Swordfish.

For a start have a look here http://www.angusj.com/sudoku/hints.php and see if the penny drops.

[eniacap]

Thanks Glyn. I don't have the problems of the guy at that link and now do understand what a swordfish is. I suppose with more experience I'll improve my technique in spotting them

[Bigtone53]

eniacap,

At the risk of annoying denis-berthier once again, one of the best ways of spotting x-wings, swordfish and above if you are a pencil-and-paper person is Arcilla's method

[eniacap]

Many thanks for the link Bigtone53, it looks at first glance to be exactly what I need.