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DB Saturday Puzzle - Saturday July 22, 2006

 
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Sat Jul 22, 2006 1:17 pm    Post subject: DB Saturday Puzzle - Saturday July 22, 2006 Reply with quote

Here is today's David Bodycombe puzzle:

Puzzle: DB072206 ******
Code:
+-------+-------+-------+
| . 3 9 | . . . | . . . |
| 7 . 4 | . . 5 | 3 2 . |
| . . . | . . . | 6 . 8 |
+-------+-------+-------+
| . . . | . 2 9 | . . 6 |
| . . 7 | 8 . 4 | 5 . . |
| 9 . . | 6 5 . | . . . |
+-------+-------+-------+
| 3 . 1 | . . . | . . . |
| . 7 6 | 2 . . | 4 . 5 |
| . . . | . . . | 8 7 . |
+-------+-------+-------+

I thought it was about standard. Warning: Hint follows!!

=

=

=

=

I got it down to a point where there is a Type 3 UR and an XY-wing which make the same eliminations in R5. This solves the puzzle, although:

There is another XY-wing lurking in the puzzle.
The UR becomes Type 4, with additional reductions available.

Keith
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Sat Jul 22, 2006 2:04 pm    Post subject: Reply with quote

Nice, both the 2 xy-wings and the 2 UR's (in fact it is one, seen as type 3 or 4) lead to the same number (partly with a box/line or box/box interaction).
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Marty R.



Joined: 12 Feb 2006
Posts: 5179
Location: Rochester, NY, USA

PostPosted: Sat Jul 22, 2006 4:02 pm    Post subject: Reply with quote

ravel wrote:
Nice, both the 2 xy-wings and the 2 UR's (in fact it is one, seen as type 3 or 4) lead to the same number (partly with a box/line or box/box interaction).

Ravel, what are box/line and box/box interactions? I suspect they might be similar to or the same as what I would call "locked candidates."

As to the puzzle, I didn't notice a second XY-Wing, but the first plus a Type 4 allowed me to complete it.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Sun Jul 23, 2006 8:39 pm    Post subject: Reply with quote

Marty R. wrote:

Ravel, what are box/line and box/box interactions? I suspect they might be similar to or the same as what I would call "locked candidates."

Yes, its the same - box/box interactions is equal to "locked candidates 2".
Quote:

As to the puzzle, I didn't notice a second XY-Wing, but the first plus a Type 4 allowed me to complete it.

Code:
 *-----------------------------------------------------------*
 | 6     3     9     | 14    8     2     | 17    5     47    |
 | 7     8     4     | 19    6     5     | 3     2     19    |
 | 1     2     5     | 3479  347   37    | 6     49    8     |
 |-------------------+-------------------+-------------------|
 | 45   -145  #38    |A37    2     9     |ab17  #1348  6     |
 | 2     6     7     | 8    a13    4     | 5    -139  -139   |
 | 9    b14   #38    | 6     5     137   | 2   #-1348 B47    |
 |-------------------+-------------------+-------------------|
 | 3     45    1     | 457   47    8     | 9     6     2     |
 | 8     7     6     | 2     9     13    | 4     13    5     |
 | 45    9     2     | 345   134   6     | 8     7     13    |
 *-----------------------------------------------------------*

With the xy-wing Aaa the 1 is eliminated from r5c89, with Bbb from r4c2 and r6c8 (gives 1 in r6c2). The UR is marked with #. The type 4 eliminates 3 from r46c8 (strong link for 8 in column 8), the type 3 (the extra candidates 14 form a triple 147 with r4c7 and r6c9) also eliminates 1 from r5c89. The 1 in r5c5 solves.
Simple Sudoku solves it with simple coloring to eliminate 1 from r5c8 (r5c5-r9c5-r8c6-r8c8) and an x-wing in 1 then (r59c59).
[edit: unintended smiley '8)' and typo corrected]


Last edited by ravel on Mon Jul 24, 2006 7:35 am; edited 1 time in total
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Marty R.



Joined: 12 Feb 2006
Posts: 5179
Location: Rochester, NY, USA

PostPosted: Mon Jul 24, 2006 1:20 am    Post subject: Reply with quote

Ravel, thanks.
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Myth Jellies



Joined: 27 Jun 2006
Posts: 64

PostPosted: Tue Jul 25, 2006 2:12 am    Post subject: Reply with quote

Here is an alternate solution which does not use xy-wings or uniqueness...
Code:
 *-----------------------------------------------------------*
 | 6     3     9     | 14    8     2     | 17    5     47    |
 | 7     8     4     | 19    6     5     | 3     2     19    |
 | 1     2     5     | 3479  347   37    | 6     49    8     |
 |-------------------+-------------------+-------------------|
 | 45   *145   38    | 37    2    *9     |-17   *1348  6     |
 | 2     6     7     | 8     13    4     | 5    #139   139   |
 | 9    *14    38    | 6     5    *137   | 2    *1348  47    |
 |-------------------+-------------------+-------------------|
 | 3     45    1     | 457   47    8     | 9     6     2     |
 | 8    *7     6     | 2     9    *13    | 4    *13    5     |
 | 45    9     2     | 345   134   6     | 8     7     13    |
 *-----------------------------------------------------------*

...the r468c268 finned swordfish in ones with the fin in r5c8 kills the 1 in r4c7. (Either the fin is true, or the swordfish is true, either way r4c7 cannot be a 1.) This is an interesting case of the finned swordfish where you can exchange the roles of the "fin" and the cell where the reduction takes place. You could also use coloring and an x-wing to crack the puzzle as well.
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