The New Sudoku Players' Forum

[MCC]

Having tried my hand at a few pappocom fiendish without using candidates, I'd thought I'd give a pappocom v.hard a go. So had the program generate a v.hard and set to work.

Using single numbers and locked candidates I managed to place eleven numbers before becoming stuck.

Thinking this is where an x-wing might be showing itself I looked for it, I found four varieties of swordfish (Of no use in moving the puzzle on), but no x-wing.

Then after spending some time on it I resorted to making a candidate list to see if I could learn something from it I could use in future.

Again, I went through the candidate list looking for something I had overlooked.The only thing I could find was a naked triple, this allowed a couple of eliminations and placements.
From there, singles and naked pairs (there might have been a hidden pair, memory fails me) solved the puzzle.

But at no time did I come across a x-wing.
Was there a x-wing that I somehow avoided?
Or was this an easy v.hard?

Code: Select all

1..|...|..8
..6|3.9|7..
.4.|...|.3.
-----------
.8.|4.1|.9.
6..|.3.|..4
.7.|2.5|.8.
-----------
.9.|...|.1.
..4|1.6|8..
2..|...|..3

MCC

[tso]

If you find all naked pairs and triples, no x-wing will be needed, though at least one can be found.

Code: Select all

+----------------+----------------+----------------+
| 1    3    5    | 7    24   24   | 9    6    8    |
| 8    2    6    | 3    15   9    | 7    4    15   |
| 9    4    7    | 6    1258 28   | 125  3    125  |
+----------------+----------------+----------------+
| 5    8    2    | 4    6    1    | 3    9    7    |
| 6    1    9    | 8    3    7    | 25   25   4    |
| 4    7    3    | 2    9    5    | 16   8    16   |
+----------------+----------------+----------------+
| 7    9    8    | 5    24   3    | 246  1    26   |
| 3    5    4    | 1    27   6    | 8    27   9    |
| 2    6    1    | 9    478  48   | 45   57   3    |
+----------------+----------------+----------------+

There is an x-wing in 5s at r59c78, but you'll still at least a naked pair to continue.

[Animator]

There is an x-wing in 5s at r59c78, but you'll still at least a naked pair to continue.

Just as you can find an x-wing in most puzzles... But there usually is an 'easier' move... Or it falls under another description.

The X-wing you described matches for example the locked candidate 5 in column 9.

The real question is (I suppose): Do you need to use the X-Wing technique to solve a Very Hard puzzle?

And the answer to that is No. If an X-Wing is needed then it is rated as Very Hard. But not every Very Hard puzzle needs an X-Wing. (The way the difficulity level is assigned is a much more difficult proces)

[Heuresement]

MCC, sorry about the delay in replying, but I have been trying to do several v.hard puzzles without using any candidates or pencilmarks. I was unable to do your above example without using candidates, and have also tried to do the last two Superior Sudoku puzzles in the Sunday Times (London). I can now spot obvious x-wings without using pencilmarks, but still have problems with triples and well hidden doubles.

My only real success with the v.hard ones without candidates was when I printed out what I thought were 2 hard ones, and after I had solved them without using candidates, I discovered that they were in fact Pappacom very hard ones! I put that down to luck more than skill, as obviously some puzzles with the same ratings are more difficult/easier than others.

If anyone better is able to do consistently the Pappacom very hard ones without using candidates or any pencilmarks, I would like to know.

[MCC]

Heuresement, well done on the v.hards. So far I've not had much success on them, although I've not tried many(without using candidates).
My problem is my short term memory, it's so short it's virually nonexistent.
Anyways, I'll keep trying, maybe one day I'll solve one.

MCC