## Newbie solving technique

Advanced methods and approaches for solving Sudoku puzzles

### Newbie solving technique

Hi
Sorry I arrive late at this game.
However, could someone describe the technique I am using.
Seems failproof, no guess work even on the difficult ones (does take a lot a fun out of solving theses).

Here's an attempt at explaining what I am doing:

(1)I divide each little square into 9 smaller square- similar to your phone pad...
(2)If a number , eg 5, is present, I check all the 5's in that column, row and 3X3 area.
(3)Do that for all numbers given.

Most of the time, it's then just fill in the blank, and it's done.

On the harder ones,
(4)I look at each tiny column/ row I created on the phone pad, and usually there is one number in the phone pad that is obvious, because all the number in that tiny row or column are already checked, and repeat the procedures (1) to (2) all over again.
(5) Fill in the blank on the phone pad and solve each phone pad row/ column individually.

Eg:

Nick70 wrote:
Animator wrote:I can see one thing you guess about and that is the cell you chose.

You normally (or atleast I) look at a specific number, row, column or box, but never on one particular cell.

I can't believe I'm reading something like this. This really looks like a denial phase.

Animator wrote:I'm not sure on this yet, but I'm begining to believe that for each 'Trial and Error'-case there is a 'Foreched chain'-case.

This isn't so. Up to now, I've compiled about 18,000 problems. About 12,000 can be solved using common techniques. About 2,000 can be solved using advanced coloring (which includes swordfish and foreched chains). About 4,000 my program still cannot solve without guessing (9 times in one case).

Note: I haven't yet implemented naked/hidden triples in my program so this changes a bit the figures above.

Should anyone be interested in the 9-guesses problem, here it is; I don't expect it to be solvable by logic.

Code: Select all
`..1.9.8.5.326.....4.............5.....3.1.6.....4.............4.....712.8.9.6.3..`

Once you have done step (1) and (2),
then r6,c6 can only be =6,
fill in slowly the phone pad for r6c6 and see what other number becomes obvious.
etc...

Or I'm I off somewhere?
Last edited by fathom on Sun Jul 31, 2005 10:59 pm, edited 1 time in total.
fathom

Posts: 8
Joined: 29 July 2005

This looks like a nice graphic way of solving by exclusion - but I suspect it'll meet it's match with grids that require more advanced logic! - have a look at some on this site that need x-wings and swordfish to solve - and do let us know how it works out! (and after the 6 @R6C6 - what next?)
stuartn

Posts: 211
Joined: 18 June 2005

### Re: Newbie solving technique

Nick70 wrote:Should anyone be interested in the 9-guesses problem, here it is; I don't expect it to be solvable by logic.

Code: Select all
`..1.9.8.5.326.....4.............5.....3.1.6.....4.............4.....712.8.9.6.3..`

That was a long time ago. Now I know it can be solved with forcing chains.
Nick70

Posts: 156
Joined: 16 June 2005

Thanks,
will look into some other one and report back.
fathom

Posts: 8
Joined: 29 July 2005

By the way, could you give me a new example of an extreme one to solve, ideally having to guess, to see whether my technique still works.
Thanks
fathom

Posts: 8
Joined: 29 July 2005

I was given this link before the site crash.
http://www.paulspages.co.uk/sudoku/sudokugallery2.php?r=outlaw
I could not do the first one in its entirety without more involved techniques.
However, for everything else published (ie not outlawed) so far that I tried, it seems to work fine.
Warning, very tedious, mindless and not enjoyable.
fathom

Posts: 8
Joined: 29 July 2005

I found someone who uses the same technique (he explains it a lot better)
http://www.sudoku.org.uk/discus/messages/2/71.html?1121515983

The only difference, is where he is stuck and has to start guessing.
I just go from each row/ column/ 3x3, in each dial pad from 1 to 9, see if that is the only one not marked, if so, then that's the number. And so on. No guessing (except for outlawed as discussed earlier). No fun, I can push paper at work...

I'm back to doing them without marking.
fathom

Posts: 8
Joined: 29 July 2005

### Newbie solving technique

fathom wrote: ".....Here's an attempt at explaining what I am doing:

(1) I divide each little square into 9 smaller square - similar to your phone pad..."

Hi fathom - I would appreciate more help The puzzle grid contains nine 3X3 boxes with each box containing nine cells. In your above explanation could you please explain what a "little square" means?

Regards Bonsai Cec
Cec

Posts: 1039
Joined: 16 June 2005

123
456
789

would be one cell of the 3x3
I took the shortcut of putting an x instead of numbers.
eg, a '6' would look like this:

XXX
XX
XXX

on an easy puzzle, once you marked all the given numbers, usually there is at least one cell looking like above, and you just have to fill in the blank with a number.

Alternatively in this row, column 2 has to be '4':

_X_ |X_ X|_ XX||X_ _|XX_|_ XX||XXX|_X X |_ _X
X _X|_X_ |X_ X||XXX |X_ _|X_ X||X_ X|X_ _ | XXX
_X_ |X_ X|XXX ||_ _ _|_XX|XX_ ||_ X_ | _ _X|XXX

Hope that helps
fathom

Posts: 8
Joined: 29 July 2005

Blimey - all looks a bit latin to me.
stuartn

Posts: 211
Joined: 18 June 2005

I'm obviously misunderstanding, but why don't you just fill in all the possibilities and see which ones, etc...

Karyobin

Posts: 396
Joined: 18 June 2005

I guess it would come to the same thing.
When you eliminate a possibility down the road, you cross it out, presumably with an x, so I just start with x and leave the possibility blank.
fathom

Posts: 8
Joined: 29 July 2005