## beginner really trying but still needs help!

Advanced methods and approaches for solving Sudoku puzzles

### beginner really trying but still needs help!

help?

(1245) 3 (124) (478)(1589)(4579) (789)(68)(469)
(45) 7 8 2 (59) 6 3 1 (49)
6 9 (14) (3478)(138) (47) (78) 5 2

(28) 5 7 9 (23) 1 4 (68) (36)
(12489) 6 (1249) (34) (235) (245) (89) 7 (139)
(149) (14) 3 6 7 8 5 2 (19)

3 8 (169) 5 (269) (29) (12) 4 7
7 2 5 1 4 3 6 9 8
(149) (14) (1469) (78) (2689) (279) (12) 3 5

What a mess, can you help quide me to the next step? thanx.
sfddoc

Posts: 17
Joined: 14 August 2005

Not valid again...Can you post the original puzzle?
RickM

Posts: 22
Joined: 18 August 2005

wow, how can you tell not valid?

original:

--- --- ---
-78 2-6 31-
69- --- -52

--7 9-1 4--
-6- --- -7-
--3 6-8 5--

38- --- -47
-25 1-3 69-
--- --- ---

9-1

4--
sfddoc

Posts: 17
Joined: 14 August 2005

I dubbed it into the program downloaded from this site. Click "verify" and it says it's not valid.
RickM

Posts: 22
Joined: 18 August 2005

The original puzzle is invalid, according to the program.
RickM

Posts: 22
Joined: 18 August 2005

### 2005-09-04 Chicago Tribune and LA Times

That's the sudoku from the 2005-09-04 (Sunday) Chicago Tribune and LA Times.
See http://forum.enjoysudoku.com/viewtopic.php?t=1458
r.e.s.

Posts: 337
Joined: 31 August 2005

I can't say for sure, but apparently it is not solvable without guessing (forcing chains are a form of guessing according to Pappacom), so Pappacom considers it invalid.

That works for me. I'm not interested in exercising my trial and error abilities
RickM

Posts: 22
Joined: 18 August 2005

RickM wrote:I can't say for sure, but apparently it is not solvable without guessing (forcing chains are a form of guessing according to Pappacom), so Pappacom considers it invalid.

That works for me. I'm not interested in exercising my trial and error abilities

Calling forcing chains "invalid" is like calling a perfectly valid mathematical proof "invalid" on the grounds that most humans (who are not mathematicians) could have created it only by trial & error.

It would be more correct to say that the logic (with no T&E) required to solve this puzzle may be too tedious for almost everyone. Forcing chains are a form of strictly deductive logic, not a form of "guessing" -- but searching for them can be very tedious.
r.e.s.

Posts: 337
Joined: 31 August 2005

RickM

A puzzle is valid -- regardless of what the Pappocom software says -- if it has a unique solution. If the program called it tuna fish, you still couldn't make a sandwich from it. Wayne did not invent Sudoku and cannot define what is and isn't a valid Sudoku. This has an ongoing disagreement between most of the world and Wayne. Apparantly, even some of the Japanese originators of the puzzle disagree with him on this subject. Some of us have been solving Sudoku since before Wayne ever heard of them -- and we don't think puzzles like this are invalid, nor will everyone require trial and error. There's a simple word for this type of puzzle -- difficult.

Forcing chains are no more trial and error than naked or hidden singles. It is SEARCHING FOR forcing chains that might be refered to as trial and error -- but the same thing can be said for searching for each and every other pattern, including naked and hidden singles. It depends on how you go about looking for the pattern.

Lots of other software will load this puzzle just fine and verify that it has one and only one solution.
tso

Posts: 798
Joined: 22 June 2005

I think I may have misspoken. This is what the help file says:

"Some publishers produce puzzles which cannot be solved with logic but need guessing or trial-and-error.

Solving a puzzle with a guess is not as satisfying as solving a puzzle with logic and reasoning.

For a computer, trial-and-error puzzles are easy. It is just a matter of blasting the puzzle with every possible combination of numbers. Teaching the computer to use logic is a more difficult thing.

Trial-and-error puzzles are not often found in print. However, they are very common among puzzles on the Internet.

There is a blurred area between logic and guessing. There are some extreme techniques which can pass as logic, but which involve making multiple assumptions until one of them proves right or wrong.

Technically these can be called valid puzzles, but at Pappocom we regard them as unsatisfying and unfair.

This program knows how to solve and verify these unfair puzzles, but it does not allow them to be included among its own original puzzles."

I agree that a forcing chain (that does not require more than one assumption) is an extension of techniques like X-wing and Swordfish. I assumed that only those puzzles requiring multiple assumptions were what the program flags as invalid. I don't know if that's a correct assumption or not. I also associated the statements above with the term "forcing chain." Attribute that to the fact that I'm a newbie and still learning the lingo...

So... back to the puzzle in question... Can it be solved with logic?
RickM

Posts: 22
Joined: 18 August 2005

Luckily for me, I appear to have the same sensibilities as Wayne as regards what I like in a sudoku puzzle and what I don't. I can see, I suppose, how forcing chains aren't strictly trial and error (since there's no error step involved) but there is a quality about it that doesn't satisfy me somehow. It just seems so similar to T&E to actually perform, even if it's not so similar from a theoretical standpoint, that I don't see the appeal in doing one but not the other.
PaulIQ164

Posts: 533
Joined: 16 July 2005