dailysudoku.com :: View topic

dailysudoku.com
Discussion of Daily Sudoku puzzles

FAQ

Memberlist

Usergroups

Profile

Swordfish.

dailysudoku.com Forum Index -> Other puzzles

View previous topic :: View next topic

Author

Message

wapati

Joined: 10 Jun 2008
Posts: 472
Location: Brampton, Ontario, Canada.

Posted: Wed Apr 15, 2009 7:57 pm Post subject: Swordfish.

I can see lots of patterns here but a swordfish makes a very nice shortcut.

Code:

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

storm_norm

Joined: 18 Oct 2007
Posts: 1741

Posted: Wed Apr 15, 2009 10:40 pm Post subject:

Code:

.---------------.---------------.---------------.
| 278 37 3-8 | 9 247 5 |A248 6 1 |
| 1 9 6 | 8 234 23 | 24 7 5 |
| 278 4 5 | 1 27 6 | 3 89 29 |
:---------------+---------------+---------------:
| 6 U58 7 | 345 9 13 |U158 2 34 |
| 4 U58 9 | 235 6 123 |U158 358 7 |
| 3 2 1 | 45 8 7 | 6 59 49 |
:---------------+---------------+---------------:
| 78 37 2 | 6 5 4 | 9 1 38 |
| 5 6 F38 |E23 1 9 | 7 4 238 |
| 9 1 4 | 7 D23 8 |B25 C35 6 |
'---------------'---------------'---------------'

this isn't needed for the solution but there is a nice UR inference present.
the UR {5,8}r45c27 has only 5 and 8 in the floor cells, so this means that any 5 or 8 external to the UR in column 7 would destroy the UR.
in this case the 8 at A and the 5 at B fit that bill in fact at least one has to be true, extend that a little and we get...

UR58[(8}A = (5)B] - (5=3)C - (3)D = (3)E - (3=8}F
and this eliminates 8 at r1c3

tlanglet

Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills

Posted: Thu Apr 16, 2009 4:31 am Post subject:

The name of the puzzle influenced my approach to this puzzle.

Code:

*--------------------------------------------------*
| *278 37 38 | 9 *247 5 | *248 6 1 |
| 1 9 6 | 8 234 23 | -24 7 5 |
| *278 4 5 | 1 *27 6 | 3 89 ?29 |
|----------------+----------------+----------------|
| 6 58 7 | 345 9 13 | 158 2 34 |
| 4 58 9 | 235 6 123 | 158 358 7 |
| 3 2 1 | 45 8 7 | 6 59 49 |
|----------------+----------------+----------------|
| 78 37 2 | 6 5 4 | 9 1 38 |
| 5 6 38 | 23 1 9 | 7 4 238 |
| 9 1 4 | 7 *23 8 | *25 35 6 |
*--------------------------------------------------*

While looking for a swordfish on <2>, I found the pattern marked "*" in r139c157 plus an extra <2> in cell r3c9 marked "?". I believe that this is a "Sashimi Swordfish" since the extra/misplaced digit is in the row and box used by the swordfish, but maybe it is a "Kraken Swordfish". In any case, I eliminated the <2> in r2c7. Am I correct or did I score on a 50/50 chance?

To finish the puzzle, I used a xy-wing 238 with a pivot <28> at r1c7 and a pseudo-cell <23> and a transport,
a finned x-wing <3>,
a x-wing <3>, and
a BUG+1.

Ted Question

ttt

Joined: 06 Dec 2008
Posts: 42
Location: vietnam

Posted: Thu Apr 16, 2009 5:38 am Post subject:

storm_norm wrote:

Code:

IMO, I’m not sure for applying AUR here by bilocated 1’s r45c7. we can find deductions based on the considering UR(58)r45c27 but can’t present it as AURs. In this case, your move can write: (8)r1c8=(18-5)r45c7=5r9c7…

ttt

daj95376

Joined: 23 Aug 2008
Posts: 3854

Posted: Thu Apr 16, 2009 5:44 am Post subject:

tlanglet wrote:

The name of the puzzle influenced my approach to this puzzle.

Code:

Ted: finned Swordfish -- the integrity of the Swordfish is not affected w/o <2> in [r3c9].

Now, what do you see if you'd used [r2] instead of [r3] in the Swordfish?

storm_norm

Joined: 18 Oct 2007
Posts: 1741

Posted: Thu Apr 16, 2009 7:06 am Post subject:

Quote:

ttt,
I see what you are saying.
you are saying that because the 1's exist in r45c7 that the UR doesn't technically exist?
right?

that looks like a type 2 UR except the 1's don't make any eliminations as a type 2 would normally do.
I was told that this pattern isn't really a UR in another thread on another forum. hmmmm

tlanglet

Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills

Posted: Thu Apr 16, 2009 1:07 pm Post subject:

daj95376 wrote:

Ted: finned Swordfish -- the integrity of the Swordfish is not affected w/o <2> in [r3c9].

For me, the unique circumstance about this pattern is that a swordfish does not require a digit in all three rows/cells, whereas a x-wing has exactly four digits plus a possible fin. I had considered viewing this as a finned swordfish, but having a fin without an associated digit seemed very odd, but a digit in a different position, like a Sashimi, made sense.

Maybe the actual name is not that critical given the details of the situation are provided so others can view and understand it.

daj95376 wrote:

Now, what do you see if you'd used [r2] instead of [r3] in the Swordfish?

I saw this condition, but assumed that it was not a valid swordfish since it only had a single digit in col1. Without the digit in r1c1, I would view is as three interacting x-wings, two of which are finned.

Ted

ttt

Joined: 06 Dec 2008
Posts: 42
Location: vietnam

Posted: Thu Apr 16, 2009 2:14 pm Post subject:

storm_norm wrote:

I see what you are saying.
you are saying that because the 1's exist in r45c7 that the UR doesn't technically exist? right?

Yes, can’t present it as AURs on proof. Of course, that’s only my opinion.

storm_norm wrote:

that looks like a type 2 UR except the 1's don't make any eliminations as a type 2 would normally do.
I was told that this pattern isn't really a UR in another thread on another forum. hmmmm

Player’s Forum? I haven't read all of it yet. In fact, I don’t know exactly types of UR (type 1, 2, 3…). I only consider the concept of AUR (internal, external or both).

ttt

daj95376

Joined: 23 Aug 2008
Posts: 3854

Posted: Thu Apr 16, 2009 2:56 pm Post subject:

tlanglet wrote:

daj95376 wrote:

Ted: finned Swordfish -- the integrity of the Swordfish is not affected w/o <2> in [r3c9].

The name isn't critical, but you did ask. The integrity of a Swordfish is maintained as long as there are two base set cells in every cover set after the fin(s) are removed. Each of your columns contains two cells from the rows and, thus, meet this condition. However, I will admit that my first opinion was of a Sashimi Swordfish.

tlanglet wrote:

daj95376 wrote:

Now, what do you see if you'd used [r2] instead of [r3] in the Swordfish?

Oops!!! I saw candidates where they didn't exist. Yes, [r2] and [r9] form a finned X-Wing for the elimination at [r3c5]. Embarassed

wapati

Joined: 10 Jun 2008
Posts: 472
Location: Brampton, Ontario, Canada.

Posted: Fri Apr 17, 2009 1:25 am Post subject:

tlanglet wrote:

The name of the puzzle influenced my approach to this puzzle.

Code:

You have a finned swordfish there.

When I solved this one I must have eliminated a candidate as I filled in the grid, I usually do notice x-wings and some xy-wings as I work. Of course URs but I like to leave them in case they can be extended.

Anyways, this has a finned swordfish on 3s as the shortcut.
Visible from above. Only needs an xyz or an xy to finish.

I did think it was a plain sword, sorry!

Display posts from previous:

	dailysudoku.com Forum Index -> Other puzzles	All times are GMT
Page 1 of 1

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum