NZ Herald Hard Fri 9 Sep 2005 - needs trial & error?

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NZ Herald Hard Fri 9 Sep 2005 - needs trial & error?

Postby retep » Sat Sep 10, 2005 11:16 am

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.
retep
 
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Joined: 10 September 2005

Postby MCC » Sat Sep 10, 2005 2:34 pm

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
 
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Postby MCC » Sat Sep 10, 2005 3:12 pm

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.
MCC
 
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Joined: 08 June 2005

re: NZ Herald 2005.Sep.9

Postby Pat » Mon Sep 12, 2005 10:17 am

.


retep wrote: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 }


.
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Pat
 
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Postby retep » Mon Sep 12, 2005 10:48 am

Pat - many thanks for pointing this out so simply and clearly.
Now it looks obvious!
retep
 
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Joined: 10 September 2005


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