## Sudoku Diagonals

For fans of Killer Sudoku, Samurai Sudoku and other variants

### Sudoku Diagonals

There can be su dokus where the diagonals also have different letters, right? What are your thoughts?
Finlip

Posts: 49
Joined: 15 July 2005

This has been discussed before several times, here, here, and in a more complicated sense, here.

Sudoku's that require the two main diagonals to have one of each digit are a long time common variant, appearing on a regular basis in most Japanese Number Place magazines.

Here's an example:

Code: Select all
` . . . | 4 . . | . 2 .  . . 7 | . . 6 | . . 9  . 9 . | . . 1 | . . . -------+-------+------ 9 . . | . . . | 3 6 .  . . . | . . . | . . .  . 1 4 | . . . | . . 8 -------+-------+------ . . . | 1 . . | . 4 .  7 . . | 2 . . | 5 . .  . 2 . | . . 8 | . . .  `

Without the additional stipulation that the two main diagonals are each an additional "group" along with each row, column and box, the puzzle would not be solvable.
tso

Posts: 798
Joined: 22 June 2005

Nice puzzle, tso! I like the color chains snaking along diagonals.
Do you have some more?
Scott H

Posts: 73
Joined: 28 July 2005

This one was really fun, bringing a new dimension to the candidate elimination!

Thanks!
Anette

Posts: 55
Joined: 09 June 2005

Scott H wrote:Nice puzzle, tso! I like the color chains snaking along diagonals.
Do you have some more?

There are two here.

This one is rows, columns and diagonals ONLY -- no boxes. Not really Sudoku without the boxes, just a latin square.
Code: Select all
`3 . . . 1 . . . 6. 2 . 6 . 9 . 1 .8 . . . 3 . . . 24 5 . . . . . 2 7. . 2 . . . 8 . .6 4 . . . . . 9 81 . . . 6 . . . 5. 8 . 2 . 6 . 4 .2 . . . 8 . . . 9`
tso

Posts: 798
Joined: 22 June 2005

The Daily Mail has cottoned on to this and they have started publishing them, naming them Su Doku X.

They have also released a book, which can be found here

Does anyone know if generally these puzzles are easier or harder than normal Su Doku?
heebiejeebieclub

Posts: 6
Joined: 15 August 2005

So far, I have no reason to believe that they are easier or harder per se. They should be slightly harder to *construct*. In a magazine of 150-200 puzzles, there will usually only be a handful that use diagonals, so the variety of difficutly is less. You probably won't one find one published in a Japanese magazine that's tougher than a Pappocom "Hard"

This Chistopher Monckton is quite the braggart. He claims that he invented these "new and ingenious" Sudoku-X puzzles that I've been solving in Japanese magazines for 2 decades.
tso

Posts: 798
Joined: 22 June 2005

tso wrote:This Chistopher Monckton is quite the braggart. He claims that he invented these "new and ingenious" Sudoku-X puzzles that I've been solving in Japanese magazines for 2 decades.

he didn't exactly claim that he invented them in that synopsis
(written by Andrew Lownie ?)
But they might want the reader to think this, I haven't read the
book. There should be an introduction in it mentioning the historics.
Anyone here has the book ?

Wow, Christopher Monckton wrote a book about sudoku.
"100 all-new puzzles" .
I wonder whether they were created by computer...
"you don't need to know any mathematics ...
...they will like quoting CM to their math-teacher
"cell-by-cell analysis of Christopher Monckton's own
route to the solution"
..which is supposedly better than any other route ?!

yeah, Chris, these evil computers and mathematicians defect
the best puzzles. Maybe you were born 50 years too late.

(CM is wellknown for his "millenium puzzle" which he
claimed could never be solved by a computer
- that error did cost him his part of a million-price)

Guenter.
dukuso

Posts: 479
Joined: 25 June 2005

From: http://www.andrewlownie.co.uk/books/monckton.christopher/index.shtml

"Christopher Monckton, inventor of Sudoku X..."

Oh, and is "Eternity" puzzle didn't "exploit a previously-unnoticed wrinkle in the laws of mathematics". That's just silly. There was nothing special about it -- just another of polyform puzzle with nothing to distinquish it from 100 others. It isn't difficult to create a polyform puzzle with hundreds of pieces that will be next to impossible to solve.

http://www.mathpuzzle.com/eternity.html
tso

Posts: 798
Joined: 22 June 2005

tso wrote:From: http://www.andrewlownie.co.uk/books/monckton.christopher/index.shtml

** ahh yes, that page. Is it written by Lownie ?

"Christopher Monckton, inventor of Sudoku X..."

Oh, and is "Eternity" puzzle didn't "exploit a previously-unnoticed wrinkle in the laws of mathematics". That's just silly. There was nothing special

**yes. "Laws of mathematics" are the same as before

about it -- just another of polyform puzzle with nothing to distinquish it from 100 others.

**well, it's algorithmically interesting, though. But that was not intended
**someone wrote his thesis about it

It isn't difficult to create a polyform puzzle with hundreds of pieces that will be next to impossible to solve.

**not so easy to determine how _next_ , apparantly

http://www.mathpuzzle.com/eternity.html

** and Eternity II is probably not under development
** I assume Lownie got that from another old article
dukuso

Posts: 479
Joined: 25 June 2005

tso wrote:This Chistopher Monckton is quite the braggart. He claims that he invented these "new and ingenious" Sudoku-X puzzles that I've been solving in Japanese magazines for 2 decades.

I just found, that someone wrote that he "owns the copyright".

That makes me wonder whether several people can "own"
the copyright for the same thing.
Or maybe he bought it from those Japanese magazines.

Now, does that mean that from now on everyone who wants to
publish a X-sudoku needs a permission from him ??
and publish a blacklist with all these evil copyright owners ! ;-)

http://www.amazon.co.uk/exec/obidos/tg/stores/detail/-/books/0755315014/reviews/026-6629832-8543613

Christopher Monckton invented the best-selling, £1-million Eternity puzzle and has sold 500,000 puzzles worldwide. He is the creator of Sudoku X, a development of the worldwide phenomenon Sudoku, for which he owns the copyright.
dukuso

Posts: 479
Joined: 25 June 2005

dukuso wrote:"He is the creator of Sudoku X, a development of the worldwide phenomenon Sudoku, for which he owns the copyright."

Quite pathetic, advertising that he owns a copyright. Big whoop. His copyright is obviously for the NAME "Sudoku X". He cannot possibly have any rights to the particular construction -- you and I are free to create, distribute and sell Sudokus with Diagonals -- we just can't use the goofy name "Sudoku X". They seem to be banking on the lay public not knowing this to make it look exclusive somehow.

Don't expect of find any hard ones either. He seems to be following the "all these puzzles can be solved by logic, not guessing" crowd therefore creates puzzles that can be solved using only the most rudimentary logic.

Oh, and don't expect anyone to buy something like this from a Japanese magazine -- they just take it. The name Nikoli holds the copyright to the word "Sudoku" in Japan, so all the other publishers in Japan don't use that word for their puzzles, calling them Number Place or similar names. They're the same puzzles. Nikoli didn't think to get the International copyright, so the rest of the world isn't restricted from using the word.

There are many better variations -- such as IRREGULAR GROUPS, DISJOINT GROUPS and EXTRA GROUPS -- seehere and here. I'm sure they'll be co-opted as well, given dorky, copyrighted names like "Mega-Sudoku" and sold as "exclusive new inventions" by white men.
tso

Posts: 798
Joined: 22 June 2005

Seems to be a little attitude creeping into that post...
PaulIQ164

Posts: 533
Joined: 16 July 2005

There's a fun diagonal puzzle with just 9 givens and an additional twist here. The givens are
Code: Select all
`+---+---+---+|...|.7.|.6.||...|...|...||2..|...|...|+---+---+---+|...|...|...||.9.|.5.|...||...|...|1..|+---+---+---+|..4|...|...||...|...|...||...|..3|8..|+---+---+---+`
The additional twist is an initially given naked group of size N in each block, where N is the single initial given in each block. See the source for the exact initial naked groups.

It was a fun puzzle, solvable by elementary techniques (no X-wings or chains required) but not at all trivial. The diagonal constraints are required several times. Have fun!
Scott H

Posts: 73
Joined: 28 July 2005

I've really been enjoying diagonal sudokus from Menneske's site here. You can choose your preferred difficulty level. I like the "Harder" level, which is the hardest level with any diagonal puzzles available
Scott H

Posts: 73
Joined: 28 July 2005

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