Sudoku Puzzles

ok

Are the tough ones solvable without guessing at any stage?

most of the tough ones need guessing...
i think it was designed that way. without
guessing but somehow difficult to solve
it would be put in hard category...
am i right?

Are the tough ones solvable without guessing at any stage?

I think so too.

Some trial and error guessing is unavoidable.

I don't believe that the tough can be solved without guessing. I have asked this question before and had no response from the administrators of this site yet.

9:29

Hi,
The tough one of yesterday 09/11 was solvable without guessing. See the proof on comment on yesterday's archive.
I've solved some other tough ones here, always found them only with logic, without guessing... BUT takes me usually some hours.
gb

5 mins 48secs..... i think i deserve a pat on the back..... i dnt think it is possible to win without a certain amount of guessing.

7:38

Hi,
The tough one of yesterday 09/11 was solvable without guessing. See the proof on comment on yesterday's archive.
I've solved some other tough ones here, always found them only with logic, without guessing... BUT takes me usually some hours.
gb

Think the tough ones are impossible without the odd clue here and there. I have never managed one without a clue

Hi Everyone,

GB - Great proof! If I have some time tomorrow, I will try and put it in an easy-to-read format and put it on it's own page so others can benefit. Again, thanks for taking the time. Contact us by email if you want to post another proof, and we can give you a format to fill them More...

I never guess and have been able to solve all tough ones I have tried. I haven't tried all, but the many I have I could figure out.

I love the new buttons - especially the clear all possiblities - makes it so much quicker and lots more fun.

But .... it would be good if when one More...

SL - I agree with the 'shading finished numbers' suggestion (as i do it on paper when searching...), it could even be more comfortable if each number 'n' was indexed by mentioning how many 'n''s are still to be placed (as i also do it on paper when searching...)...
gb

tough ones are solvable without guessing, but they can become time consuming

7:27 on tough today. Got interupted during my train of thought. Hate that.

Today i'm a little slow... 8:51!!!
But is good thought.

It would be great if John Butler, Tiago, or Liam could indicate by what 'train of thought' they can solve so rapidly such puzzles. I'm AMAZED and willing to learn from them !
gb

hahahaha 3.58

I solved today's puzzle without guessing, but at one point there were 4 possibilities for one square. If either of two choices were correct, the solution would NOT be unique - so I eliminated those two. Is this type of logic 'cheating'?

The tough ones usually take me 30 minutes. What are some hints on getting to do it faster? Do you still enter all the possibilities? Do you print it out or do it online?

It would be great if John Butler, Tiago, or Liam could indicate by what 'train of thought' they can solve so rapidly such puzzles. I'm AMAZED and willing to learn from them !
gb

sorry for duplicate comments. Seems that 'reactualiser' (F5) sends the message again...

22:21 It would have been faster if i was not interupted by either my co-workers or the wife.

21:42

It is not a sudoku if you have to guess. You should never have to guess or the maker of the puzzle sucks.

9:01

GB-thanks a million for your guidance which i am sure will benefit all sudoku lovers.

4days, 13hrs, 42mins, 17secs

i love the sudoku. i've set a trend in my school to do them, and every morning there is a rush to the papers. whoever made them up is a legend in my book.

gb - Care to provide a proof for this puzzle? I would be very interested to see how it can be done without guessing. Thanks.

Scott : yes this one is solvable by logic and I agree with AC : 'It is not a sudoku if you have to guess'.
Just a bit long to put it in words. I'll try when I get enough time. Wait and see !

Thanks gb, looking forward to it.

For Scott : here is a way out (I hope there are straighter ones...).
I name cells by two coordinates [column,row], the left bottom one being [1,1]. I name blocks like this:
789
456
123.
If there is a more standard notation in sudoku world, please let me know.
1) First simples More...

continued...
2)16 are the only choices in [1,1] and in [2,1], so you can eliminate all

1s and 6s except these as possibilities in row1 and block1.
Perform the same with the only choices :
89 in [7,8] and [7,9],
36 in [8,9] and [9,9],
28 in [5,1] and [5,9].
3) you should More...

continued...
4)Again simple eliminations lead to
[2, 5]=6, [4, 6]=3, [5, 8]=3, [1, 1]=6, [1, 4]=1, [2, 1]=1, [5, 4]=5, [5,

2]=1, [8, 5]=5, [9, 7]=5, [8, 8]=1, [9, 3]=1. Cheerio, 41 cells filled, 40

left...
5) Now 248 are the only ones able to fill [4,8],[5,9] and [6,8], More...

7)Last effort... you should now stay with only choices 28 in [5,1] and [5,9], 35 in [1,3] and [2,2], 47 in [1,6], 37 in [1,7], 24 in [1,9], 58 in [6,3]. What if [1,3]=5? then [6,3]=8, [5,1]=2. What if not? then [1,3]=3, [1,7]=7,[1,6]=4, [1,9]=2, [5,9]=8, [5,1]=2. In both cases : [5,1]=2.
8) From now on, you surf right to total solving by simple eliminations.

Thanks for the explanation gb

I hope someone will find an easier proof... There must be a lot to learn...