The New Sudoku Players' Forum

[RW]

tso, nice swordfish puzzle, but unfortunately as daj95376 pointed out, the swordfish isn't "extreme" enough for this thread.

As daj95376 also pointed out I made some modifications to the list. If anybody else has any suggestions of puzzles that should be moved to some other category, please notify me and I'll have a look at it.

Mike, I haven't had time to look at the last of your puzzles yet. I won't be around for a week now, but I will try to test them when I get back.

RW

[Ocean]

I'm not completely clear on what qualifies as an EE, but this puzzle:
[...]
... posted minutes ago in a thread called "Best Ever Swordfish Sudoku?" requires only Swordfish and singles. However, the Swordfish is needed as the very first move, making it not-so-effortless. I infer from the rules that a puzzle is supposed to need more than merely the one advanced tactic to qualify, but many of the puzzles in the thread contradict this. Someone else decide if this belongs -- and either way, we need a Swordfish on the list.

Nice swordfish puzzle, tso. Think it will be a good contribution to the 'Superior plus' thread recently started by 'ab'.

Here is an attempt on an effortless nice loop (or alternating inference chain):

Code: Select all

 *-----------*
 |..1|.23|..4|
 |...|..1|...|
 |5..|...|6..|
 |---+---+---|
 |...|...|.73|
 |6..|...|..5|
 |89.|...|...|
 |---+---+---|
 |..4|...|..9|
 |...|6..|...|
 |1..|75.|8..|
 *-----------*

 *--------------------------------------------------------------------*
 |-79     6      1      | 8      2      3      |#57     59     4      |
 | 3      4      79     | 5      6      1      | 27     29     8      |
 | 5      28     28     | 49     479    47     | 6      3      1      |
 |----------------------+----------------------+----------------------|
 | 4      125    25     | 129    8      6      | 129    7      3      |
 | 6      127    237    | 12349  13479  247    | 1249   8      5      |
 | 8      9      237    | 1234   1347   5      | 124    12     6      |
 |----------------------+----------------------+----------------------|
 |#27    #578    4      | 123    13     28     |#135    6      9      |
 | 29     58     589    | 6      134    248    | 135    15     7      |
 | 1      3      6      | 7      5      9      | 8      4      2      |
 *--------------------------------------------------------------------*
The bidirectional chain tells that there has to be a 7 in either r1c7 or r7c1.
Therefore 7 can be eliminated from r1c1.


[RW]

I received a review from Mike Barker and made some more modifications to the list. I also separated BUG-lites and Layered BUG-lites into their own categories.

Ocean, nice puzzle with a nice UR that solves it:

Code: Select all

 *--------------------------------------------------------------------*
 | 79     6      1      | 8      2      3      | 57     59     4      |
 | 3      4      79     | 5      6      1      | 27     29     8      |
 | 5      28     28     | 49     479    47     | 6      3      1      |
 |----------------------+----------------------+----------------------|
 | 4      125    25     | 129    8      6      | 129    7      3      |
 | 6      127    237    | 12349  13479  247    | 1249   8      5      |
 | 8      9      237    | 1234   1347   5      | 124    12     6      |
 |----------------------+----------------------+----------------------|
 | 27     578    4      | 123   *13     28     |*135    6      9      |
 | 29     58     589    | 6     *134    248    |*135    15     7      |
 | 1      3      6      | 7      5      9      | 8      4      2      |
 *--------------------------------------------------------------------*
r78c7<>1

There's also a nice (but unnecessary) BUG-lite+2 in r348c23 (r4c2<>2 and r8c3<>5).

I think there's already too many UR puzzles on the list, so I won't add this puzzle there right now. I think the amount should be reduced somehow, but I'm not quite sure how yet. Any ideas?

RW

[ronk]

r78c7<>1

I see r8c6<>1 (because of conjugate links in r8 and c7 for digit 3) ... but what's the deduction for r7c7<>1?

I think there's already too many UR puzzles on the list, so I won't add this puzzle there right now. I think the amount should be reduced somehow, but I'm not quite sure how yet. Any ideas?

All else being equal ... discard the ones that weren't submitted as URs?

[RW]

I see r8c6<>1 (because of conjugate links in r8 and c7 for digit 3) ... but what's the deduction for r7c7<>1?

The deduction is related to the UR I described here. There's no strong links for '1', but still if r7c7=1, then r8c5 becomes a hidden single. The strong link on '3' and the pair takes care of the rest.

Code: Select all

     b
abZ=====abX
-----------
abY C   ab
bD  bE  abF
bG  bH  abK

All else being equal ... discard the ones that weren't submitted as URs?

That thought has slipped through my mind, that could be a good way to reduce the list without upsetting anybody.

RW

[daj95376]

Wow! I guess that I'll never understand much more than UR Type 1. I know it's going to end up being one of those

Code: Select all

3 | 1
-----
1 | 3


patterns that still confuse me. Fortunately, I see

Code: Select all

[r7c7]=1 => [r8c8]=5                         => [r1c8]=9
         => [r7c5]=3 => [r7c4]=2 => [r7c1]=7 => [r1c1]=9


and that gives me [r7c7]<>1.

[ravel]

I guess that I'll never understand much more than UR Type 1.

Most "exotic" UR eliminations (maybe despite of the type 3 ones) can be comprehended easily with simple chains, that lead to a deadly pattern like your 3-1-3-1 (only note that none of the numbers must be a given, then, whenever this pattern arises, the solution cannot be unique).
For the examples above:

Code: Select all

r7c7=1 => r7c5=3
          r8c7=3
          r7c45 <> 1 => r8c5=1

r8c7=1 => r8c5=3 => r7c5=1
          r7c7=3

BUG-lite+2 (deadly patterns vertically 8-2-5--2-5-8 and 2-5-8--8-2-5)
r4c2=2 => r3c2=8 => r3c3=2 => r4c3=5
                              r8c3=8 => r8c2=5
r8c3=5 => r8c2=8 => r3c2=2 => r3c3=8
          r4c3=2 => r4c2=5


[ronk]

Without using a strong link (for r7c7<>1) ...

r8c5-1-r8c8-5-(AUR:r78c7=5|4=r8c5) implies r8c5<>1

... solves the puzzle too.

[ravel]

Thats nice, though a bit cannibalistic

[fermat]

I tried 3 solvers with this one of mine. One saw colors and solved it, another found it easy except for a BUG and the third claims a jellyfish.

Does it qualify as a BUG or big fish?

Code: Select all

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


[ronk]

Thats nice, though a bit cannibalistic

By that definition, even a UR Type 1 is cannibalistic.

[ravel]

Yes, but what was odd to me (and i enjoyed) was, when i read it from left to right, that the 1 in r8c5 "destroys" the UR, that is used afterwards to show that it cannot be there.
In a UR type 1 you would not argue this way.

Also a deadly pattern chain would not have this feature:
r8c5=1 => r6c6=5 => r8c7=3 => r7c7=1 => r7c5=3

[ronk]

Yes, but what was odd to me (and i enjoyed) was, when i read it from left to right, that the 1 in r8c5 "destroys" the UR, that is used afterwards to show that it cannot be there.

Interesting, as I never picture any candidates within a loop as removed ... until after the loop is closed at a discontinuity. Maybe I need to solve puzzles without pencilmarks once in a while.

In a UR type 1 you would not argue this way.

My working definition of a "cannibalistic" deduction: A "cannibalistic" deduction occurs whenever the candidate excluded is within the pattern (or chain) causing the exclusion ... no matter how the deduction is expressed. With that definition, a UR Type 1 qualifies.

[ravel]

To be honest, i hoped to see Havard say something like
HOW UGLY: The 1 eats it's UR eats it's 1

[RW]

One saw colors and solved it ... Does it qualify as a BUG or big fish?

1. It shall not be solvable through use of the following techniques alone:

-locked candidates
-pairs, triplets, quads (naked or hidden)
-x-wing, swordfish
-colors, multiple colors
-xy-wing

So I'm sorry, it doesn't qualify.

I've added some more of Mike's puzzles to the list and got two new categories, ER and Franken Swordfish. Then there was also the first UR puzzle I didn't manage to solve by myself (#36). There is at least 5 different URs that allow eliminations (and a BUG-lite) but if you aren't careful, you'll easily destroy the one needed to solve the puzzle... The wrong URs will only take you to a XY-wing or a BUG+1. Nice puzzle!

RW