The New Sudoku Players' Forum

[retep]

A friend and I have independently worked on this, eschewing trial and error. We each get as far as 46 numbers and then are stuck. Trial and error easily solves the puzzle from there but I understood that it is not supposed to be necessary.

I have got to:

**76*82*1
*652**3*8
2*8*4**6*
721*368*4
85342****
64981**32
*76*8*425
5*2**49**
9*4**2***

and have enumerated the possibilities for each remaining cell.

Please advise. Thanks.

[MCC]

There is a swordfish in 5's in cells:

(r1c5)(r1c8)(r4c4)(r4c8)(r9c4)(r9c5)

This enables you to eliminate the 5 in cell (r6c7) leaving a 7 to be placed.

[MCC]

Ignore the above, although there is a swordfish, the 5 in (r6c7) cannot be eliminated.
But the 5 in (r3c4) can be eliminated because either (r4c4) or (r9c4) must be a 5.
Not really sure that it helps move the puzzle on.

[Pat]

.

I have got to 46:

Code: Select all

 . . 7 | 6 . 8 | 2 . 1
 . 6 5 | 2 . . | 3 . 8
 2 . 8 | . 4 . | . 6 .
-------+-------+------
 7 2 1 | . 3 6 | 8 . 4
 8 5 3 | 4 2 . | . . .
 6 4 9 | 8 1 . | . 3 2
-------+-------+------
 . 7 6 | . 8 . | 4 2 5
 5 . 2 | . . 4 | 9 . .
 9 . 4 | . . 2 | . . .

• box Middle-Middle needs a 7, which can only go in c6; eliminate 7 elsewhere in c6
• c5 needs a 9, which can only go in box Top-Middle; eliminate 9 elsewhere in TM
  

thus the list of possibilities for r2c6 is reduced from { 1,7,9 } to just { 1 }


.

[retep]

Pat - many thanks for pointing this out so simply and clearly.
Now it looks obvious!