After posting

http://freepages.misc.rootsweb.ancestry ... 20dots.pdf I was too chicken to look at the forum, too worried about what sudoku experts might say. Have only just got back to it now.

enxio27 wrote:You are confusing solving AIDS with solving TECHNIQUES. Pencil marks, dots, etc. are solving AIDS, but they are NOT techniques, or strategies, to solve a puzzle. Quite frankly, your writeup doesn't make a whole lot of sense to anyone who is reasonably experienced with solving sudoku. I think you need to familiarize yourself with known techniques and fully comprehend them before you are in any position to add your own.

OK, "aids" rather than "techniques" or "strategies" if it makes you happy.

999_Springs wrote:how about this one

- Code: Select all
`795|6..|8..`

81.|.95|.76

.46|.87|.95

---+---+---

67.|8.9|.5.

92.|56.|78.

.58|.7.|6.9

---+---+---

56.|7..|9.8

.37|9.8|56.

.89|.56|..7

49 clues. SE rates it 10.4. thanks to dobrichev for the puzzle

The first thing I did was simplify the look of it, replace all 5,6,7,8,9 with X and, because only four numbers remain unfilled use the dot method placement for four unknowns rather than for 9 unknowns.

You're right about two things. First, the "line guess" method I described doesn't suffice on its own. Second, it's a remarkably difficult Sudoku for so little fill-in.

I solved it in about 1 hour, which is about twice as long as I normally need to solve an average Black Belt Sudoku (ie. Level 3 and above).

There are 24 possibilities for Row 1. Try all 24. 14 are quickly eliminated leaving 10. For each of the 10 in turn try all possibilities for Row 8. That's all it took.

Pat wrote:mollwollfumble wrote:

If there are more than 28 [given] digits in the puzzle

then it’s likely to be very easy

really?

here's a little collection of

742 puzzles having 39 cells given,

tell me if

any of them is "very easy"

here's an example — not a puzzle i would ever try —

- Code: Select all

. . . | . . . | . . 1

. . 2 | . 1 3 | . 4 5

1 4 . | . 2 5 | 3 6 .

-------+-------+------

. 2 4 | . 7 8 | . 5 .

5 7 . | 3 . 2 | . 8 4

8 . . | . 5 . | . . .

-------+-------+------

. 8 . | . . 7 | . 1 .

2 . 7 | . 8 1 | 4 3 .

4 1 . | 2 3 . | . . 8

I timed the solution to this one (I don't normally time Sudokus). 1 hour and 8 minutes.

The first thing I did was to fill all the blank cells using the method of complete dots I posted earlier. That took 8 minutes. Then I wasted time listing all possibilities for Row 7 (too many possibilities) and Row 9 (too few possibilities) before settling on Row 4 with Row 9 as a backup. I tried all eight options for Row 4 before finding the solution.

I've noticed in the past that whenever anyone posts what they claim is a difficult Sudoku, somebody else comes along and says "no, I found it easy". Well, I didn't find those two easy, but I didn't find them very difficult either. Perhaps there aren't any difficult Sudokus.