Tough Sudoku

Fi - you have definitely excelled yourself here. What a beautiful photo - well done.

Would that be in the Arnhem Land area?

12:26 Lotsa big birds -- squawk! :)

8:58 Maen

Oh... beautiful picture! a lot of bird life. 35:34 not too bad today.

one more, thanks NICK for your reply yesterday.

Beautiful shot, Fi.

8:11 Way too easy for a tough

Possible proof of too easy sudoku of 10 11 06:

1) Start at 22 filled - the given puzzle. Unique Possibilities to 26 filled. (UP 26).
2) Hidden pair 24 at hi8 forbids d8=2,ab8=4,h8=15 and i8=157 UP 49
3a) Locked 7's at e56 forbids d6=7
3b) Locked 6's at e456 forbids df4=6
3c) Hidden pair 67 at f18 forbids f1=3 and forbids f8=9
3d) Locked 9's at d78 forbids d24=9 UP 50
4) fc on 3's: f6 == g6 -- i4 == i3 forbids f3=3 UP 81
Sets: 8. Max depth 2. Rating: .12 - trivial



Alternative to step 3)
e6=7 == e6=8 -- e3=8 == e3=9 -- f3=9 == f3=3 -- f6=3 == g6=3 forbids g6=7 UP 81
Sets 6, md 4, rating .16 -

After the easy Hard, this one stumped me.

Since today's puzzle is not quite tough enough, imho - I would love some feed back on the following puzzle that I created:
080_095_000
905_000_007
000_060_000
820_100_000
300_600_090
001_200_300
100_320_000
260_007_080

I am thinking about making a custom puzzle generator that will attempt to require certain types of rarely used techniques. I think, perhaps, that the techniques are rare because:
1) There seems to be a preference for symetrical puzzles - which limit some of the possible complexities.
2) There seems to be a tendency to discard puzzles that require the rare techniques.

The puzzle above probably has many manners of solution. I have a proof that is depth 5, total of only 8 sets - but it is not obvious.

rather straight for a tough!

Hi, Steve-- Your creation appears to be missing a row. Very difficult, indeed!

I solved today's Tough Puzzle! It seems it is not really tough. Was interesting, though!

After your step 2, i eliminated to the end. This was too easy :-)))

In the puzzle you created there are only 8 rows??

My above comment was for Steve - sorry!

6:30 I fill in the blanks then use the check moves. That might be cheating but it works. It'll never work on paper though.

Good evening to all!

Fi: A great picture> When I come to Australia I hope you will be available to take my guide and I aroung the NT for a few days!

Very pretty photo; it looks familiar

hehe don't know how I lost a row!

The last row:
000_000_000 - row 1
sorry about that!

Here is the full puzzle:

080_095_000
905_000_007
000_060_000
820_100_00 0
300_600_090
001_200_300
100_320_000
260_007_080
000_00 0_000

I guess that since the last row did not contain any candidates, I just did not even see that I omitted it. Of course, without knowing which row I omitted, one would have some problems with the puzzle.

Nice picture but very easy puzzle today.

I am very curious, if anyone wishes to indulge me, in the manner of solution others find for the puzzle I posted, hopefully correctly this time. Rather than give away the technique I intended to highlight, I would love to see if there are other simpler ways to solve the puzzle - versus the technique it was intended to expose.

Today's puzzle was simple enough that I had time to finish my proof of the 10-08 puzzle.

Hi STEVE from Ohio,
Your puzzle, i looked pairs (47) and sovle it. that way is correct?

Hi ttt!
There always many ways to solve a puzzle. Without more information and what you did with the pairs, I cannot tell... The puzzle does look like it might beg remote pairs, but I cannot find the links without looking a long, long time.
Perhaps you can tell us a more detailed explanation of what you found?

I ran the puzzle I created through the Sudoku solver at the scanraid site. After a long, long time, it could do no better then to solve one square more than the given puzzle, and a bunch of eliminations that evnetually just got the solver stuck. So, perhaps it is an interesting puzzle?

Here is a possible path for the puzzle with which I have troubled this site:

Possible proof of 'medium' sudoku created on 10 11 06:

1) Start at 23 filled - the given puzzle. Unique Possibilities to 23 filled. (UP 23).
2) Hidden pair 12 at gi5 forbids g5=4578 and forbids h5=458 UP 24
3a) Locked 6's at ac9 forbids ghi9=6
3b) HALS cross ALS logic:
S1={Almost hidden triple 123 at h1789}
S2={g9=124,i9=1234}
123 almost weak across the sets: Thus forbids:
acdh9,g78,i7=4 and forbids h1=4567 and forbids g78=12 and forbids i7=123
UP 81

Sets: 2+1+5 = 8
Max depth 5 at step 3b
Rating: .35 - not truly tough at all!


3b) as an fc like animal:
h1=123 == {Locked 12, Locked 13, or Locked 23} at h789 -- (12,13 or 23} at gi9 == {Pair 14, pair 24 or pair 34} at gi9
Note: This is a three way wrap around chain, thus we have:
h1=123 and pair 4x (x=1 or 2 or 3) at gi9 and 123 locked into h789gi9 which forbids:
acdh9,g78,i7=4 and forbids h1=4567 and forbids g78=12 and forbids i7=123

3b) Better exposed as a matrix:
h1=1 h789=1 000000 000000 0000
h1=2 000000 h789=2 000000 0000
h1=3 000000 000000 h798=3 0000
0000 g9=1__ g9=2__ 000000 g9=4
0000 i9=1___i9=2___i9=3___i9=4
Each row is a strong set. 5 truths at least in the matrix.
Each column is mutually weak - no more than one truth in each column - no more than 5 truths in the matrix.
Therefor, exactly 5 truths in the matrix - one in each column and one in each row.
Thus, each column must be a strong set!

Steve give solution?

Hi STEVE from Ohio,
I was wrong and ... thoughtless. i just see 47 on a179,d79 then filled d1=9, i forgot 5 ...
Sorry, i must be thinking much more before put the comment here.

Did Gath know it was my birthday and that I wouldn't have the time to spend on a challenge today ! This one needs nothing more than colours (or F.C using only one number). Does this justify the puzzle being placed in the tough section? Sorry Steve, I'd love to look at your puzzle, but when I see ALS or 'almost' anything, or 'matrix' in a proof, I leave it alone. One day I'll feel ready to go that extra step.

Happy Birthday Meg.

Thanks for the comments re the picture. You are right HalT that that Billabong is in Aboriginal land but out in West of Darwin towards Port Keats (Wadeye). Arnhem Land is East of Darwin. I head out there next Monday.

Canuk Greg, Who is your guide?

Oct. 19, 2007.

SE=4.2

note re Steve's puzzle:
many chains solve (back-door is ghi9=4).

loop:(3=124)ghi9-(2)h78=(*12)h19-(3)h19=h78 => acd9<>4 et.al.

18:50