Sudoku Puzzles

Why put a clue in the first comment? I had to resize my browser so your clue wasn't showing while I was working on the sudoku.
Can we have a 'hide comments' button, so we don't have to have comments like these just underneath the grid?

4:48 for TOUGH....that's better!!

People who post clues should be banned

15:02 is a good time

8:50, first time trying tough so pretty happy with that.

13.23

Sorry for my bad posting. Hope a moderator can clean it, the sooner the best. It was due
1)to my opinion that the interest in those puzzles is not at all in finding one solution, but in proving uniqueness.
2) to the fact that it's not usual that a single clue 'kills' so rapidly the puzzle (i More...

with apologizing again.

My apologies also, I probably sounded a bit harsh (also resizing the browser isn't an arduous task).
As to proving uniqueness, I thought that it was a clever idea by NJ yesterday to use the fact that the puzzle is defined as being unique to exclude some of the possibilities.

Seriously, are all you people solving this using logic *only*. I thought the whole point of these puzzles was that you can work them out without guessing.

Very rarely am I ever able to solve a tough puzzle on this site without making at least one -- if not two -- guesses and taking them through to their logical conclusion on the grid.

5.31

17:03 I can do all the levels by logic, excet for Tough. Sometimes, when I have it down to just 2 numbers in one area, I have to take a gut feel and go with it.

Just done it in 5.47 not allowing incorrect moves but what fun is that - it much better taking and longer and using your own brain instead of the computers.

The 'tuff' level has exceded normal deduction methods, today as usual. I'm disappointed that the only method of solving these puzzles is to do it wrong, and correct your error. I like the 'hard' level where solutions can be proved by information given, not information that may or may not be proven wrong later.

Definitely needed to save the game a few times for this one. And, as usual, I didn't bother timing myself.

the objective is to solve the puzzle using logic to eliminate the possibilities,not by using the aids to do it for you or by guessing. all the puzzles can be solved this way. there would be no point posting puzzles that couldnt be solved without guessing

Proof by contradiction is a perfectly valid tool. That is why, when I am thoroughly stuck, I'll break up a pair and see where it takes me. I only use the Save feature so I don't have to manually backtrack if I'm wrong.

For gb from France and other like-minded people I have a few notational suggestions:

1) To make it even more chesslike, use a,b, ..., i for columns (left to right) and 1, 2, ..., 9 for rows (bottom to top). So the top left corner becomes a9.

2) Write moves as a1=1 (or a1:=1 for More...

continue: at the cell a1; a1=1 %column means that a1 is the only cell in its column with possibility 1; %row and %box are defined similarly. See an example in September 15 easy section. Of course, more complicated deductions will require more complicated
comments.

Great site and getting better every day. Thanks! One suggestion that should be easy to implement: create one more button 'Create Possibilities' which places all possibilities into all the unfilled cells. Thanks in advance!

new, so i'll ask a possibly 'obvious' question - Do the solutions times posted start after all the possibilities are filled in the grid or include this 'setup' process too. by the way I love this game!

17:41 bad time and I had to guess one number cannot see how quick times can be achieved with logic alone

I am stuck after:
g8=7 %column; g5=4 %column; f9=7 %box; d2=7 %box; i9=4 %box; c3=7 %in box abc123 7 can appear only in a3 and c3, but if a3=7, there will be no room for 7 in box abc456; i6=1 %the only other cells for 1 in box ghi456 are in column h, but choosing one of them will leave no room for 1 in box ghi789; f5=1 %box;
Any suggestions?

24:27 i got stuck then it all popped open for me. sometimes this best thing for me to do is to walk away and come back with fresh eyes

I do these tough ones on a print-out rather than on-line, and spend the whole day doing 1 or 2 numbers at a time in between jobs. I love it when I can come back to it again and see something that I couldn't before.

20:09

I thought I was a pretty clever chick, until.... I found my way to this page and now realise that I am perhaps not quite as smart as I thought I was....hummm, this is doing my head in, it may take me a few days!

Hi Everyone,

I have deleted a few posts that were making the puzzle a little easy.

As for the notation, check out the proof given in the 'Proofs' section (far right in the menu). If anyonee else feels like posting a proof, just send an email and I will set them up.

Cheers, and enjoy,
Gath

I am at same position as andrei. Please explain how to logically find any next number without guessing.

Hi rick and andrei (which i adopt notations thankfully, abbreviating them in %b,%r,%c,% for %box,%row,%column,%cell ). I found a way, but not so immediate.
if i2=2 then
1)f2=6%,g3=6%b.
2)i3=8%,i7=3%,g7=6%:too much 6s in col g.
Now if h5=3, then c2=3%c,g1=3%b,i7=3%b and no more room for 2s in col i.
Hence h5=9.
Hope you can continue now.

Mistake in last comment :
if i2=2 then
1)f2=6%,g3=6%b.
2)i3=8%,i7=3%,g7=6%:too much 6s in col g.
So please wipe 2 from possibilities for i2, after which 2 and 8 fill now i3 and i7 in col i.
Now if h5=3, then c2=3%c,g1=3%b and no more room for 3s in box g7.
Hence h5=9.

I think the point is to solve via logic alone - and it can always be done, but on tough ones it usually involves wide patterns (not just within one row or column of 3x3 squares.

If I get a flashing red, or get impatient and make a deliberate guess, even if it works I don't count the More...

21:19

13:50..04/24/06

done

45:36

42 mts.

8.58