Sudoku Tutorial

Swordfish

There's a problem with swordfish that didn't exist with the X-wing.   Remember that the X-wing had to have the candidate present EXACTLY two times in each row?    Well, in the swordfish, it doesn't have to be present exactly three times in each row.   The candidate can be present TWO or THREE times in each row.  This makes the swordfish much harder to spot. In row 3, the candidate is present only twice but it still meets the criteria for a swordfish. The missing cell (r3c7) can be a solved cell for a different number or an unsolved cell with other candidates Here our candidate is present just twice in row 3 and row 6.  It still meets the definition of a swordfish. And in this example, there are no rows where the candidate is present three times.  Yet it is still a valid swordfish because the candidate is committed in each of the blue columns This is why swordfish can be very hard to find.  The good news is that I have yet to find a puzzle where finding a swordfish is the only technique left to eliminate a number from a cell.    You might have to find an XY-wing, an XYZ-wing, or perhaps a finned X-wing instead.   But if you can find a swordfish,  you'll have some well deserved bragging rights. Click here to see an example of a swordfish So, if an X-Wing is 2 by 2 and a swordfish is 3 by 3,  what's a 4 by 4, 5 by 5, 6 by 6, etc?  (read on)

Tutorial Home

Comments?  Email me!