The New Sudoku Players' Forum

[Chessmaster]

Code: Select all

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

this is a sudoku i made. people who i had solve it said it was hard. but i did not think it was that hard.

[TKiel]

Chessmaster,

I played the puzzle and it solved with nothing but singles, but I sure liked the way the grid was arranged for the initial clues. Keep on truckin'.

Tracy

[Chessmaster]

I thought it was an easy puzzle. i solved it the same way that you did.

[TKiel]

Chessmaster,

I took the liberty of removing some of your clues and adding one to the center cell, but kept it symmetrical. It seems to play a little better (from a very easy to an easy), but obviously doesn't look nearly as nice as your origional layout.

Code: Select all

 *-----------*
 |5.8|2..|6..|
 |...|.7.|..4|
 |3.4|.9.|5..|
 |---+---+---|
 |...|...|...|
 |.9.|857|.2.|
 |..2|...|8..|
 |---+---+---|
 |..5|.4.|1.6|
 |6..|.8.|...|
 |..3|..6|7.5|
 *-----------*


Tracy

[gsf]

(edit -- thanks to the future posters who note that this is an invalid sudoku)
here's a symmetric puzzle derived from the original grid
only 2 backdoors so it should be a bit challenging

Code: Select all

backdoors: [1,8]=3[7,7]=3

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


[tarek]

here's a symmetric puzzle derived from the original grid
only 2 backdoors so it should be a bit challenging

Code: Select all

backdoors: [1,8]=3[7,7]=3

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


Hi gsf,

How many solutions does this puzzle have??!!!

[Carcul]

Hi Gsf.

I think your puzzle have 90 solutions.

Regards, Carcul

[gsf]

I think your puzzle have 90 solutions.

Regards, Carcul

thanks for the kind catch
I'll have a word with my QA dept

[TKiel]

When I entered Chessmasters' origional clues into Simple Sudoku it said it was asymmetrical. I thought I knew how to recognize symmetry in a puzzle and it seems to look symmetrical in his post, so I was just wondering where the asymmetricalness(?) occurrs. I could have made an error entering it, but I checked everything at least twice.

Tracy

[gsf]

When I entered Chessmasters' origional clues into Simple Sudoku it said it was asymmetrical. I thought I knew how to recognize symmetry in a puzzle and it seems to look symmetrical in his post, so I was just wondering where the asymmetricalness(?) occurrs. I could have made an error entering it, but I checked everything at least twice.

the top and bottom horizontal bands are symmetric on the diagonals
the middle horizontal/vertical bands are symmetric on the vertical

Code: Select all

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


here is a rotational symmetric one derived from the above
this time double checked to have one solution

Code: Select all

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


[TKiel]

gfs

the top and bottom horizontal bands are symmetric on the diagonals
the middle horizontal/vertical bands are symmetric on the vertical

So one would fold it on the diagonal to compare box 1 with box 9, fold it on the opposite diagonal to compare box 3 with box 7, fold it on the vertical center to compare box 4 with box 6 and box 5 to itself and fold it on the horizontal center to to compare box 2 with box 8 and box 5 with itself?

Tracy

[gsf]

So one would fold it on the diagonal to compare box 1 with box 9, fold it on the opposite diagonal to compare box 3 with box 7, fold it on the vertical center to compare box 4 with box 6 and box 5 to itself and fold it on the horizontal center to to compare box 2 with box 8 and box 5 with itself?

right
the puzzle is not symmetric
but the observations explain why they might seem symmetric on first glance

[QBasicMac]

I thought I knew how to recognize symmetry in a puzzle and it seems to look symmetrical in his post

Just want to make sure you realize that the presence or absence of symmetry has nothing to do with whether the puzzle is valid. A puzzle that has exactly one solution is valid, symmetrical or not. Otherwise, it is invalid, again whether symmetrical or not.

Symmetry is just an esthetic thing, just as in crossword puzzles.

Mac

[tso]

Symmetry serves additional purposes. It's easier to check that you've transcribed it correctly, as a misplaced, missing or extra clue may stand out. It's easier to tell that you've already solved the puzzle. (for those of us who don't like to mark up the original)

Also, Nikoli *defined* a Sudoku as a number place puzzle with symmetricaly placed clues, so it could be argued that if the clues aren't symmetrical, it's not Coke, just cola.

However, due to language confusion, it is likely that Nikoli insisted that the clues have *order*, but not necessarily symmetry. They have published puzzles in which the clues were *not* symmetrically placed, but formed a recognizable shape, letter or kanji. They've also published some -- notably some of the 25x25 monsters -- that are *nearly*, but not quite symmetrical. This may be due to the fact that they are hand constructed and then computer checked. An extra clue or two might have been needed to ensure (1) uniqueness of solutions and (2) reasonable difficulty level. (Human solvers don't typically use more than 2 or 3 pencil marks in the 25x25 puzzles, so they have to be much easier than a 9x9 can be, mostly singles and other tactics that can be spotted without pencil marks. Still, *I've* never completed one without botching it.)

[QBasicMac]

Also, Nikoli *defined* a Sudoku as...

Who the devil is "Nikoli"?

What if I *define* a Sudoku as a puzzle with a 1 in r1c1?

Mac