The New Sudoku Players' Forum

[moggymidge]

Hi, I've been a Sudoku addict for a while now but I've only just discovered this fantastic forum - can anybody help me please

I'm just getting into some of the advanced solving techniques and I now understand (and have used) Swordfish but I'm having trouble with using 'colours'. I've looked at various web-sites, including the great 'angusj' (would definately recommend) but I'm confused - when you've established a candidate number is it important which square starts the alternate chain of colours - if it is how do you know which one to use?

[emm]

No, it doesn't matter which cell starts the chain. You can start anywhere. You can label them +/- green/blue, A/B or Mars/Venus. Until you've done the colouring you don't kow which of the conjugates are true and which are false - just that because they're conjugates, one lot will be and one lot won't.

The thing about colouring is that it allows you to draw conclusions about what you can eliminate -

if two of the same colour are in the same group then all cells of that colour are false

if an uncoloured cell intersects with both colours then that cell is false

[evert]

Some coloring puzzles:

Code: Select all

000700530796005001000002000000000010074000000003870005020010607000000380030069000
150000000009060023000090650000170000040030070008500040801000009000002000003000800
030006050609000000000200000050019003901670500000000000005004020108000000790800601
809000200000000030340501000900000050400006000002038600200090000000200800058000004
008030000000607010000000200000045803000072409090000070020004005053080940000000300
004320000000800200010006005000000000008000009900078400001000704072009300000052100
000000750100000000306098000000000403503046000021000000804000007000005002002079804
400030706090004002010000008000007900002000060080003057008000000070020001000071040
000041000420000086000000590000005000006000830103906005068100070000070000200000060


[Crazy Girl]

You might want to check out the link below, in which colouring is being discussed

http://forum.enjoysudoku.com/viewtopic.php?t=3223

If you have any more problems, please post again.

[moggymidge]

Thanks everyone, I'll give colours another try - one more question-
evert - sorry if I'm being stupid but can you explain how the rows of coding translate into a sudoku grid please??

[emm]

moggymidge - I suspect there are 81 numbers in each line which if you have very good eyesight and great powers of concentration you should be able to transpose into a 9x9 grid starting top left and moving across 9 numbers to a row. If not you could get some other puzzles on colouring from the SadMan website http://www.simes.clara.co.uk/programs/sudokutechnique12.htm

[CathyW]

If you copy one line, you can then paste directly into Simple Sudoku and, I presume, Sadman Sudoku as well.

[moggymidge]

Thank you em, thank you CathyW and THANK YOU SIMPLE SUDOKU

[Cec]

".. but I'm having trouble with using 'colours.."'

Thanks moggymidge for this thread and the helpful responses above which answer my same queries.

Cec

[evert]

If you copy one line, you can then paste directly into Simple Sudoku and, I presume, Sadman Sudoku as well.

Yep. I saw others use this format when posting many puzzles.

[yasmin]

I have one more question re. em's reply:

QUOTE:
" The thing about colouring is that it allows you to draw conclusions about what you can eliminate -

if two of the same colour are in the same group then all cells of that colour are false "

What I don't get is this: how can you say that all cells of that colour are categorically false? As far as I get it, when colouring, we don't know which colour represents "false" and which "true".
Now, As it is quite possible to have, say, 1 "true" 3 and 2 "false" 3's in a box (or row or column), than aren't we eliminating a real possibility for solution? Sure, we can't have 2 true ones and 1 false, but the opposite IS possible, or am I not getting something?

please advise,
Yasmin

[vidarino]

I have one more question re. em's reply:

QUOTE:
" The thing about colouring is that it allows you to draw conclusions about what you can eliminate -

if two of the same colour are in the same group then all cells of that colour are false "

What I don't get is this: how can you say that all cells of that colour are categorically false?

I'll answer that with an example. Here is a color map from a puzzle posted in another forum a few minutes ago;

Code: Select all

 . . . | a . . | . A .
 . . . | . . . | . . .
 . . . | . . A | a . .
-------+-------+------
 . . . | . . . | . . .
 . . . | . . . | . . .
 . . . | . . . | . . .
-------+-------+------
 . . . | . . . | . . .
 . . . | a . . | A . .
 . . . | x . a | . a .


Looking at the top row, for example, we know that exactly one of A or a is true, since they are conjugates. Continuing coloring conjugates in rows, columns and boxes we end up with an interesting situation in box 8; we get two a's. This means that if a was the true color, we would have a contradiction by having two 8s in one box. Ergo, A must be the true color.

Hope that clarified things a bit.

Vidar

[ronk]

Sure, we can't have 2 true ones and 1 false, but the opposite IS possible, or am I not getting something?

My guess is you don't yet realize ...

... if a conjugate color utlimately turns out to be represent true anywhere on the grid, it must represent true everywhere.

Ron

[yasmin]

Yes that helps, thanks for both your replies !
Yasmin

[Cec]

"...Here is a color map from a puzzle posted in another forum a few minutes ago .."

Hi Vidar, What forum was this?

Ergo,..."

If "Ergo" is jargon what does it mean? My guess would be "therefore". It isn't in my Acronym dictionary. At least learning jargon has taught me something - I can now spell "Acronym"

"..A must be the true colour.."

Am I correct in concluding that the two a's in box8 can be excluded and if so then what is the significance of the 'x' in this box?

Cec