Tuesday, 26th October 2021
Puzzles Solved Yesterday: 191
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Back after 13 years! Seeking advice
Dizzy
Kwon-Tom Noob
Puzzles: 9
Posted - 2021.04.16 07:29:34
Hi guys,

I haven't visited this site for 13 years! Nice that it's still here! Disappointed to see that it's fairly quiet - I thought by now it might grown to be huge. IMHO Slitherlink is the best game ever!

I could never understand why Sudoku was so popular! It's nowhere near as good as Slitherlink!

Well, the last time I came here, I was a total newbie and could only solve the ones in Nikoli books, which, in retrospect, are ridiculously easy! LOL

Over the last 10 years, I have developed my skills, but I've only been playing Simon Tatham's "Loopy". (I assume members here are familiar with the program? It is excellent.)

If you don't mind me saying, I prefer the way Loopy works to this site - I like that all the sides are yellow by default, and when you "cross" them they are simply blank, instead of having crosses. I personally find that a better way of playing the game. In fact, when I come back here, my brain finds it really difficult to adjust to the style here!

Over the last 10 years I've gone from Loopy's "Easy" setting, up to the "Hard" setting. I can now solve the majority of "Hard" puzzles, but there are just a few that I still struggle with. Obviously, there are still some "rules" I haven't yet worked out.

So I thought I would ask here. If I were to post some images of partly completed Loopy puzzles, would that be OK? (Given that the puzzles aren't from this site?) And would anyone be able to give me any hints?

For example, here's one I just can't finish...

Dizzy
Kwon-Tom Noob
Puzzles: 9
Posted - 2021.04.16 07:37:27
I've simplified the above image and converted it to the Kwon-Tom Loop style, which might be easier to understand for those not familiar with Loopy...


Last edited by Dizzy - 2021.04.16 11:12:28
pqg
Kwon-Tom Obsessive
Puzzles: 5267
Best Total: 15m 37s
Posted - 2021.04.16 15:00:09
Top edge of the top 2 must be an x, or else there'll be 3 lines entering the top right square. Rest of it falls out pretty easily from there.
Dizzy
Kwon-Tom Noob
Puzzles: 9
Posted - 2021.04.16 22:13:25
Ah, of course! That is a rule I'd never considered before - three lines can never enter a square!

Thank you so much! I may be back to post some more here!
qqwref
Kwon-Tom Obsessive
Puzzles: 3121
Best Total: 13m 3s
Posted - 2021.04.17 03:52:28
This idea is more general than just a single square: _any_ area must have an even number of lines enter it. In that square area, you know that 1 line enters in through the bottom right, and 1 line enters in through the bottom left; therefore, as pqg said, the top left, where a line could be, must be empty.
Dizzy
Kwon-Tom Noob
Puzzles: 9
Posted - 2021.04.17 20:51:41
OK how about this one then...? What would be my next move?



Converted to Kwon-tom Loop style:



Blank:

Tilps
Kwon-Tom Obsessive
Puzzles: 5597
Best Total: 20m 22s
Posted - 2021.04.18 01:35:26
The bottom left quarter of that puzzle can be solved statically by 'advanced logic' I think ... (finding pairs of edges that have to be opposite or equal to each other and deriving a contradiction based on two edges not being able to be both set) - but really I would just move on to 'trial and error' stage.  A single additional set edge down the bottom causes a contradiction, thus the opposite must be true.  The remainder of the puzzle looks like it'll fall out after that. (Okay maybe not all the remainder of the puzzle - I can't see that far ahead.)
Last edited by Tilps - 2021.04.18 03:34:51
Tilps
Kwon-Tom Obsessive
Puzzles: 5597
Best Total: 20m 22s
Posted - 2021.04.18 01:40:11
To be more specific, the bottom left corner there is a 3, above that 3 there are 4 two's in a square.  The top two of those two's both of their top edges can be proven equal by chain of 'these two edges must be opposite' (part of the shortest way to make the chain involves the even number of lines concept above, but it can be done otherwise). Since there is already a line between them, they can't both be set as it would make a t-junction in the loop, thus they must both be crosses.
Last edited by Tilps - 2021.04.18 01:48:27
Jankonyex
Kwon-Tom Obsessive
Puzzles: 5050
Best Total: 9m 35s
Posted - 2021.04.18 04:32:40
Quote:
Originally Posted by Dizzy
OK how about this one then...? What would be my next move?
This can be solved by coloring or simply counting lines entering the left bottom region containing 8 cells.
Dizzy
Kwon-Tom Noob
Puzzles: 9
Posted - 2021.04.18 11:03:38
Thank you all for your great advice, very much appreciated, and I will consider what you said!

As for the "trial and error" strategy which was mentioned, that is something I personally prefer not to use. There are many times when I can plainly see where the line needs to go, but I just don't feel personally satisfied unless I've solved a puzzle using "rules"
Tilps
Kwon-Tom Obsessive
Puzzles: 5597
Best Total: 20m 22s
Posted - 2021.04.18 13:07:36
Trial and *error* isn't about seeing where the line should go.  Its either about where the line can't go, or where a cross can't go.
Seeing where the line should go is good for 'trial and success', which can finish a puzzle, but cannot prove a puzzle.

Ultimately the main practical difference between something like edge-colouring and trial based contradiction finding is whether you can notate it on the puzzle without needing an 'eraser'. (Although merging edge-colouring chains derived separately might make you want an eraser if you are doing them by hand )
In this particular case the trial is almost short enough that you can probably see the contradiction in your head without ever making any notations.

I've been through phases of being strong 'constructive logic is the best logic' proponent myself, it certainly is a personal choice. But it is also not exactly a well defined boundary.
Dizzy
Kwon-Tom Noob
Puzzles: 9
Posted - 2021.04.19 20:15:02
OK, here are three more I couldn't do…

Any ideas, folks?

Puzzle 3



Puzzle 4



Puzzle 5
Tilps
Kwon-Tom Obsessive
Puzzles: 5597
Best Total: 20m 22s
Posted - 2021.04.20 00:22:20
I don't have any suggestions for 4.
3. I'm not sure how to convert it to 'constructive logic', but there is a trivial contradiction flowing from putting a cross on the bottom of the bottom most unsolved 2.  It results in an early loop close.  I'm not sure what to do next there though.
5. There is a lot of progress to be made with counting here. The right hand edge of the 2 below the pair of 3's in the top right must be a cross for instance. Once that is done there is another counting opportunity on the bottom left area. Which solves the bottom middle section.  After that the top left may fallout - if there is anything slightly tricking remaining it might be the diagonal pattern of 2's in a corner (corner appears as part of solving above) leading to a 3, which is a cascade of 'same/opposite' pairing logic which solves both the twos completely and half the 3.
pqg
Kwon-Tom Obsessive
Puzzles: 5267
Best Total: 15m 37s
Posted - 2021.04.20 00:30:45
3. 2 at B7 must have an X at the bottom or else there'll be a dead end line going into top right corner. That gives you quite a lot.

4. The 3 at C1 can't have its x on the left (because there'd be 3 lines going into top left corner) or the bottom (early loop closure with the 3 below it). That gives you a couple of lines on the lower 3, one of which interacts with the 3 along the bottom to force an x above it, and a line on the right of C1. Again, lots of straightforward progression from there.
qqwref
Kwon-Tom Obsessive
Puzzles: 3121
Best Total: 13m 3s
Posted - 2021.04.20 01:01:20
My interpretations:
3) If the A7 corner area has no line, then the 3 at B6 must connect to both the A5 and C7 areas which is impossible.  A bit trial-and-error feeling but it works.
4) A5 is entered by a line on the top-right, bottom-left, and bottom-right corners, therefore a line must exit on the top-left corner (which is the top of A4).
5) B2 is entered by a line on the top-left, bottom-left, and bottom-right corners, so there is a line exiting the top-right corner, which crosses the 2 at B2 to leave a line on the top of A3.
Sam
Kwon-Tom Obsessive
Puzzles: 2101
Best Total: 24m 39s
Posted - 2021.04.20 07:52:37
3)If there's a line between E3 & E4 that makes a corner pointing into a diagonal line of 2s, and creates a quick dead line
Sam
Kwon-Tom Obsessive
Puzzles: 2101
Best Total: 24m 39s
Posted - 2021.04.20 08:04:26
And by "3)" I mean "4)"...
Jankonyex
Kwon-Tom Obsessive
Puzzles: 5050
Best Total: 9m 35s
Posted - 2021.04.20 14:28:25
Quote:
Originally Posted by Dizzy
OK, here are three more I couldn't do…
Any ideas, folks?
3: count lines entering region A6-B7
4: count lines entering cell A5
5: count lines entering region A7-C7
Also any region with diagonal 3-2-2.. or 1-2-2.. pattern opening can have one line or cross deduced. I would suggest you to have a look at the logical thinking thread in this forum. Many (but not all) solving technique have been mentioned there.
MondSemmel
Kwon-Tom Obsessive
Puzzles: 5258
Best Total: 7m 47s
Posted - 2021.04.20 16:00:43
Here is an old thread full of tips and strategies to solve puzzles.
Jankonyex
Kwon-Tom Obsessive
Puzzles: 5050
Best Total: 9m 35s
Posted - 2021.04.20 20:31:04
Quote:
Originally Posted by Dizzy
...As for the "trial and error" strategy which was mentioned, that is something I personally prefer not to use....
Puzzles can be solved using different strategies, you can introduce many different type of markings: line and cross, virtual numbers, coloring, junction types, highlander notes etc. and discover their rules. Many years ago I created a simple solver for myself using many different logical rules with no assumption and pattern recognition needed. I introduced markings like (even corner) vs (odd corner) to handle diagonal-2 propagation and markings like (<=1 lines across a corner) vs (>=1 lines across a corner) to handle L-shape-131 pattern. They are simple and I believe there are way more advanced rules for solving difficult pattern and puzzles without any assumption. The problem is, even something can be deduced without trial and error, using too much marking notes makes puzzle extremely difficult to mark and handle, plus the rules are usually computer friendly but low efficiency for human. Therefore trial and error plus observation is still by far the most useful tool for me to finish the task. If you are interested in finding other strategic rule not found on this forum, you probably need more work and insight, and discover your own. I have created some user puzzles with Jsl prefix. Those are written by hand and have quite simple and nice logical solution, with minimal to no long assumption needed. I believe you can get many insight during solving those puzzles.

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