The New Sudoku Players' Forum

[tze26]

Hello to all out here.

I'm new to this website and are curious of how difficult a sudoku puzzle can be. Please post some "unsolvable" puzzle for me so that I can evaluate myself.

Thanks

[Shazbot]

if you do a search for "hardest puzzle" you should find a few

[Carcul]

Hi Tze26.

Welcome to this forum. Chek here for a very good puzzle. Also try exercises #5 and #6 here.

Regards, Carcul

[vidarino]

Here's one I came across that seems to put up a good fight:

Code: Select all

.5.3....9
.......86
..1....52
2..9...35
9...1....
73..8....
...27....
.7.....1.
.....64..


Vidar

[tso]

Good question. There were several lists of "hardest puzzles", but they are partially or completely obsolete based on newer tactics. There were a few that couldn't be solved by tabling and even Bowman's Bingo -- for example, this one ...

Code: Select all

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


... which Sudoku Susser calls "The Toughest Known Sudoku" ... and cannot solve it without recursion.

You'll find puzzles that will stump all or most computerized solving methods short of tabling here:

Vegard Hanssen's "Sudoku Puzzles"

(Sudoku Susser will automatically fetch puzzles from this site.)

Gaby Vanhegan "The Daily Sudoku"

"Solo", part of Simon Tatham's Portable Puzzle Collection


Also Fairly hard:

Koalog's Expert Sudoku of the Day

Astraware's Diabolical Sudoku of the Day

[tze26]

Thanks guys,

So as I had just notice, unsolvable / hardest / etc means doesn't have a straight answer, though possible to find answer with software.

I'll try them out to night after work.

By the way, When I tried some puzzle last night, I found that if in a row, column or 3x3 box has 2 cell with same 2 numbers in it, both nuimbers can be strike off in other cells of the same row, column or 3x3 box.

e.g.
34 . 34 | 346 . . | . 347 . |
. . x | x . x | x . . |

r1c4 must be "6" and r1c8 must be "7" because either r1c1 or r1c3 must be "3" and the other one "4", leaving "6" for r1c4 and "7" for r1c8.

I belief the same concept can be allpy to 3 numbers in 3 cells. Anyone has a thread that I could see more on this method ?

Best regards

[Crazy Girl]

I belief the same concept can be applied to 3 numbers in 3 cells. Anyone has a thread that I could see more on this method ?

Yes it can.

Do a search of Pairs (2 numbers) or Triples(3 numbers) or even Quads(4 numbers), and check out the links HERE and HERE for more basic/intermediate techniques