The secret of solving Sudoku

[namtrak]

And for the competitive among us, this mornings (19/6) Herald Sun Sudoku - 15:45

[Rocker]

Namtrak,

I also prefer to do Sudoku on paper rather than on a computer screen, so I print out this blank grid, to provide plenty of room for pencilmarks.

Rocker

[namtrak]

That would have to be the hardest Sudoku I have ever seen!!!

[Gingermick]

and the easiest

[Rocker]

Blokes. Sheesh cant help yourselves! Have to analyze everything down to sub-atomic level.

I love doing my sudokus, particularly the difficult ones. I reckon they take about 20 minutes. I don't enjoy doing them on computers, I much prefer the in one in the Herald Sun (particularly Thursdays). Now I am gonna be looking at it wondering if its a Swordfish pattern,or a Nishio or if there are any disjoint subsets in there. I dont need to know all that guff, I just need to know that the elimination strategies I have developed for me work me. Sheesh!

I don't think you will be able to do this fiendish one without using forcing chains: http://www.sudokuoftheday.com/pages/...?day=1&level=4 . I managed it in about 30 minutes, but had to use that technique.

Rocker

[namtrak]

12

I gotta get a life

[Alastair]

Alasdair,

Surely, it is far easier to do the puzzle if you have unchecked 'Allow incorrect moves'; that setting makes it unnecessary to employ advanced tecniques such as forcing chains, when you are deadlocked. I usually take 30 minutes or so to do a hard Sudoku, but I don't cheat by letting the computer do all the hard work.

Rocker

Yeah Dave, point taken!

However, like Namtrak says, I do them for fun, and not as some major challenge. Keeping the "Allow incorrect moves" unticked does not mean that I use it to solve by trial and error. It is mainly to pick up the "idiot factor" mismoves that crop up.

I also only do up to "HARD" usually, where it is very seldom that you need to go with forcing chains, as the logic methods of elimination are usually sufficient, 8 /10 times.

I don't take it seriously enough to put up with the frustration of proceeding through a further dozen moves, only to find a mistake. If that happens, I would usually laugh it off. As it is, if I get the dreaded flash of red, and it is not "finger trouble" I mentally write the result off, and finish the rest as an exercise only.

regards

[Rocker]

Did anyone do today's 'diabolical' sudoku from http://www.sudokuoftheday.com/pages/about.php ? I got a valid solution, but it differs somewhat from the solution given on that site for the puzzle. I though Sudokus were supposed to have a unique solution.

Rocker

[joe greiner]

Did anyone do today's 'diabolical' sudoku from http://www.sudokuoftheday.com/pages/about.php ? I got a valid solution, but it differs somewhat from the solution given on that site for the puzzle. I though Sudokus were supposed to have a unique solution.

Rocker

I don't think that's necessarily true, although I'd be more inclined to believe it if it was actually stated. I've found at least one where a last empty pair could be interchanged. More than that would indicate something haywire in either the problem statement or my "solution," I think.

Joe

[Rocker]

I don't think that's necessarily true, although I'd be more inclined to believe it if it was actually stated. I've found at least one where a last empty pair could be interchanged. More than that would indicate something haywire in either the problem statement or my "solution," I think.

Joe

Joe,

It is actually stated in Sudopedia: "A well-formed Sudoku has a single solution that can be found by reasoning, regardless of the complexity of that reasoning."

My solution to the diabolical sudoku for July 7th is mostly the same as the solution given, but 13 cells differ; there are three digits transposed in rows 4, 6, and 7, and four digits transposed in row 5. In the columns, there are two digits transposed in columns 2 and 9, and three transposed in columns 4, 5, and 6.

Rocker

[joe greiner]

Joe,

It is actually stated in Sudopedia: "A well-formed Sudoku has a single solution that can be found by reasoning, regardless of the complexity of that reasoning."

My solution to the diabolical sudoku for July 7th is mostly the same as the solution given, but 13 cells differ; there are three digits transposed in rows 4, 6, and 7, and four digits transposed in row 5. In the columns, there are two digits transposed in columns 2 and 9, and three transposed in columns 4, 5, and 6.

Rocker

I mis-stated the anomaly I found. It was actually two empty pairs IIRC.

Consider a fragment:

x x x A x x B x x x
x x x Z x x C x x x
x x x B x x A x x x

A and B can be swapped willy-nilly from two remaining candidates without violating the requirements, as far as I can tell, but I might have to re-examine it if I can find it. The get-out-of-jail-free card is "well-formed." The puzzle-writing algorithm might have a hiccup; or not, of course.

I haven't visited the site in your link; too many other things on my Works-In-(non)Progress list.

Joe

[Alastair]

Did anyone do today's 'diabolical' sudoku from http://www.sudokuoftheday.com/pages/about.php ? I got a valid solution, but it differs somewhat from the solution given on that site for the puzzle. I though Sudokus were supposed to have a unique solution.

Rocker

Hi Dave,

Within some limits, this is not completely true.

I have a whole book of puzzles, and almost every one has 2 solutions----------- usually a 4-square pair reversal.

regards