The New Sudoku Players' Forum

[GracieAllen]

Brand new, shiny member, trying to improve my solving for hard puzzles…

Is there a sudoku solver that solves puzzles the way a human does – as in it DOESN’T start with all the possible candidates revealed? I've used the Sudoku Solver by Andrew Stuart (sudokuwiki), but it's of limited help because it STARTS at the brute force point, with all the candidates.

I’ve been doing Sudoku for a little while and medium puzzles are usually pretty easy. With hard puzzles I’m about 30% successful solving without going to the brute force method of finding all the available candidates.

I’ve been watching people at Cracking the Crypto (CTC) solve “hard” puzzles, and they frequently imply that you should be able to solve hard puzzles without brute force or any of the strategies more complex than X-wing, Y-wing, maybe a swordfish (very rarely). I’m using Snyder notation – probably some modified version (similar to CTC as far as I know). I only mark cells where a number can go in 1 of 2 cells. Those get marked in corners. If I’m solving a cube, row or column, those go in the center of the cell. I have the basic techniques down pretty well except when I have some sort of lapse and miss something obvious.

I've also watched a number of other people on Youtube solving "hard" puzzles and they also RARELY need anything beyond the very basic skills the CTC people use. I, on the other hand, get most of my hard puzzles from sudoku.com, and find that about 1 in 3 is straightforward to solve without brute force to find the one number in the right place that unlocks everything.

So in the end is this just a matter of slogging through a few hundred hard puzzles or are there people that just "see" the patterns and can spot the cell that cracks the puzzle, and the rest of us are doomed to be "bad solvers" or maybe mediocre at best?

[Pat]

depends a lot on how they define "hard"...

http://paulspages.co.uk/sudoku/

[GracieAllen]

Is the difficulty generally based on the number of given filled cells, or is there some other, or additional, criteria? I've been doing the hard puzzles from several newspapers and they haven't required any of what I think of as brute force where you just fill in every possible candidate in the whole puzzle then look for inconsistencies. But the hard puzzles I get from sudoku.com often do. The people at CTC that solve puzzles have commented that newspaper and/or human generated hard puzzles are usually not as difficult as computer generated puzzles...

[Pat]

Code: Select all


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



this is Medium

do you agree?

8..34..2.2........34.7....1.3...9..5...16.734.64....1......3.6..1......2...25.19.
[ play ]

[Pat]

Code: Select all


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



a little tougher?
would you call this Hard?

[ play ]

[Yogi]

Brute Force is something that is usually done by computers. Maybe what you are calling BF would be referred to in this forum as Trial & Error. T&E is pretty close to guessing, which is generally regarded as anathema.
Anyway, the so-called ratings which are labelled with terms such as Easy, Hard, Very Hard, etc., can vary so much that they are virtually meaningless when you try to compare those from different programs. That’s why mostly in this forum they use numbered SE ratings. These come from a program called Sudoku Explainer. However, there is more than one version available and it seems that the one which can be downloaded from GitHub is the most accepted. Mine comes from SourceForge and it gives different results.
While it is generally true that puzzles which start with fewer givens or clues are harder, this is not always the case. The program I use rates these four puzzles as Simple, Easy, Moderate and Fiendish, even though they all start with only 17 givens:

000020050600000010300080000020040700010000000000300000506100000000700002000000800
000020050700800000000000000000050960400000700000001000000700802065300000010000000
000020054008010000070000300000050020030600000000000000000300607200400000100000000
000020050600000100000004000042030000000800600000000010570100000000000302000600000

The rating of a puzzle is usually related to the types of elimination techniques which are necessary to solve it, beyond those initial moves which are called Basics, which are also called Singles. Singles are Cells which can be filled only by one possible value or candidate (all others having been eliminated) or are the only Cell in a given House where that Candidate could be placed. The rating is a measure of the difficulty or complexity of the non-basic moves which will be required after all Singles have been placed.
There is a very old but valid thread in this forum called Solving Without Pencilmarks, listed under Advanced Solving Techniques, which you may find useful. Most of the Solvers you can download or access online have an option to show or not show the candidates for the unsolved cells. The most useful and understandable YouTube videos I’ve seen are those of Sudoku Swami in his Complete Course, although you may choose to watch his Pencil & Paper series.

[GracieAllen]

Thanks for the replies...

Pat, yes the first puzzle was pretty straightforward, and solvable using things I’m familiar with. I don’t know how difficult it would be classified as.
The second puzzle stopped me dead, and I had to resort to putting in all the candidates. It still caused me problems because I haven’t gotten good at finding the techniques for hidden/naked triples and quads. Once I got the hidden pair (23) and the naked quad (I had to use the solver to find that), it fell apart.
I’ve tried learning how to find the triples and quads, but haven’t hit on an explanation yet that worked for me. I tried “sudocue” (I think), but their explanation left me puzzled as did a couple others. I’ll have to keep looking for an explanation and examples that I “get”…

Yogi, my terminology is probably faulty here. My “brute force” is what I think of when I get stumped and have to go through the whole Sudoku and fill in the candidates. Once that’s done, unless the puzzle is one that is beyond my skillset, it’s just a matter of running through the numbers and the puzzle is pretty easy to solve.
I’ve scrupulously avoided using trial and error other than mentally sometimes doing the “if cell X is 2 then cell Y has to be ? and that means cell Z has to be whatever”.
I didn’t realized there even WAS something called Sudoku Explainer. I just downloaded the SourceForge 7z file but so far I have no idea how to make it run – the txt files I’ve looked at so far are gibberish to me. I went and got the one from Github. That one at least I can get to work.
I’ll go out and see if I can find the Sudoku Swami youtubes.

But, back to my original question… Is there a solver that DOESN’T immediately put all the candidates on the puzzle and immediately start solving using knowledge a “normal” user wouldn’t have?

[yzfwsf]

But, back to my original question… Is there a solver that DOESN’T immediately put all the candidates on the puzzle and immediately start solving using knowledge a “normal” user wouldn’t have?

My solver can do it, it has pencile-paper mode.

[Yogi]

How does one access yzfwsf's Solver ?
What is it called?

[Pat]

back to my original question… Is there a solver that DOESN’T immediately put all the candidates on the puzzle and immediately start solving using knowledge a “normal” user wouldn’t have?

i gave you one link
in my first reply;

and added a "play" link
in later replies.

try them?

[Pat]

How does one access yzfwsf's Solver ?
What is it called?

YZF_Sudoku

[philvo]

Hello GracieAllen,
My solver at http://sudokugeant.cabanova.com has pencil-like functions.
You can enter digits or short texts in cells, write notes next to the grid, undo-redo, etc.
The solver is developed with EXCEL. If EXCEL is installed on your PC, you can download and use it.
Phil

[GracieAllen]

Sorry Pat. I didn't even see the "Play". I just grabbed the <whatever the line of 81 characters is> and pasted it into SudokuExchange - that's what I've been using for solving all my puzzles.

I'm now trying the "Play" that uses "The Daily Sudoku". And figure out how to get it to do a step-by-step solve showing what it's doing like the Sudoku solver does, but without all the candidates.