The New Sudoku Players' Forum

[DreamCH]

After some 400 puzzles I finally see the easier things and can do the ones rated hard (www.websudoku.com) pretty fast.

But the ones called "evil" are still beyond my skills!

How to get that far? I`ve to say that I struggle whenever a number has to be fixed which has too much possibilites open. How to learn the advanced stuff step by step?

Thanks and greetings from Switzerland

DreamCH

[ab]

I have written software that might help you understand these strategies:
hidden and naked sets, locked candidates, x wings, swordfish, jellyfish, xy wings and xyz wings. It highlights the candidates that cause the eliminations. It might help you along the road:
uk.geocities.com/aidan_001/software.html { broken link }

Then of course there's Mike Barker's excellent post:
http://forum.enjoysudoku.com/viewtopic.php?p=21804#p21804

[RW]

Hi DreamCH

In my experience the websudoku Evils don't require anything more than hidden/naked subsets. You can study the naked/hidden pairs/triplets here.

RW

[sudokusimon]

Hi DreamCH

You can try different levels on i.e. www.gosudoku.eu
in fact there are 10 levels of difficulty

[Pat]

You can try different levels on
www.gosudoku.eu

there are 10 levels of difficulty

so i twice tried their toughest level — "level 10" —

Code: Select all

+---+---+---+
|.45|.83|...|
|.3.|4.5|..2|
|...|7..|...|
+---+---+---+
|3..|6.1|8.9|
|28.|...|..7|
|..9|.37|6..|
+---+---+---+
|4.7|.5.|...|
|51.|...|.4.|
|9..|...|...|
+---+---+---+

Code: Select all

+---+---+---+
|35.|...|.97|
|..6|...|...|
|942|..8|3..|
+---+---+---+
|...|2..|...|
|.2.|631|9.8|
|.8.|7..|...|
+---+---+---+
|76.|...|.3.|
|...|..4|2.5|
|.3.|.1.|64.|
+---+---+---+

— as you can see, both are solved by "hidden singles"

[fermat]

Pat, you were luckier than I. #182655, which I got, has two solutions.

Code: Select all

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


Edited to add:Oops, as Pat pointed out I missed a clue.
R2C6 is a given 3. The puzzle is valid, but easy.

[Pat]

#182655 has two solutions

Code: Select all

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


no, not quite — #182655 has one more clue r3c6 = 3, and only one answer.

Code: Select all

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

sorry i neglected to note the puzzle-numbers on my earlier examples.
here's one more example from their "level 10" — #85435 —

Code: Select all

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

— like the others, all it needs is "hidden singles"