The New Sudoku Players' Forum

[elmerfudd56]

Am looking for help on a puzzle. This is the point where I am stuck:


5 _ 6 | _ _ 4 | _ _ 2
3 4 1 | _ 7 2 | 5 6 _
2 _ 8 | 5 6 _ | 4 _ _


8 2 7 | 3 9 5 | 6 1 4
4 5 9 | 1 8 6 | 7 2 3
1 6 3 | 4 2 7 | _ _ 5


7 _ 4 | 6 _ 9 | 2 _ _
9 1 2 | 7 _ _ | _ _ 6
6 _ 5 | 2 _ _ | _ _ 7

Any help would be greatly appreciated. Thanks!

[Ruud]

Hi,

Here are your remaining candidates:

Code: Select all

.---------------.---------------.---------------.
| 5    79   6   | 89   13   4   | 1389 3789 2   |
| 3    4    1   | 89   7    2   | 5    6    89  |
| 2    79   8   | 5    6    13  | 4    379  19  |
:---------------+---------------+---------------:
| 8    2    7   | 3    9    5   | 6    1    4   |
| 4    5    9   | 1    8    6   | 7    2    3   |
| 1    6    3   | 4    2    7   | 89   89   5   |
:---------------+---------------+---------------:
| 7    38   4   | 6    135  9   | 2    358  18  |
| 9    1    2   | 7    345  38  | 38   3458 6   |
| 6    38   5   | 2    134  138 | 1389 3489 7   |
'---------------'---------------'---------------'

The crossing of box 3 and column 9 allows you to remove some 9's, but you may already have done that.

Row 8 reveals a subset.

If you know how to use coloring, try using it on digit 1, this may be the breakthrough you need. After that it's singles only.

Ruud.

[elmerfudd56]

I had to look up "coloring" instructions, and I think I understand them. Please let me know if I got this right.
Looking at the 1's in r1c5, r1c7, r3c9, and r7c9 will let me cross out the possibility of there being a 1 in r7c5, which then means that r7c9 must be a 1. Thanks so much for your help!

[emm]

This puzzle came up in the Non Pappocom thread. This explains the colouring.

Look for conjugate pairs – just 2 of that number in any row, column or box. Label the numbers alternately – say red and blue. Because they’re pairs, either the reds or the blues will be correct.

The first rule is that if you find two of the same colour in the same group then they are the incorrect ones.

The second rule is that if you find an uncoloured candidate that intersects with a red and a blue that is also incorrect (that doesn't happen in this case).

Code: Select all

 .   .   .   |  .  1r  .  |  1b   .   . 
  .   .   .  |  .  .   .  |  .   .   . 
  .   .   .  |  .  .  1b  |  .   .   1r 
-------------+------------+------------
  .   .    . |  .   .  .  |  .   .   . 
  .   .   .  |  .   .  .  |  .   .   . 
  .   .   .  |  .   .  .  |  .   .   . 
-------------+------------+------------
  .   .   .  | .   1r     |  .   .   1b 
  .  .   .   |  .  .   .  |  .   .   . 
  .   .   .  |  .  1   1r |  1r   .   . 

Since two reds end up in same group - both box 8 and row 9 - they must be false and you can eliminate all the red 1s.

[Cec]

This particular post is an example of the dilemma which I find at times in deciding what form of assistance is appropriate to a "first or second-time poster" whose sudoku skill level is unknown to me.

When initially joining the forum, my knowledge of solving techniques was basically zero. The forums were interesting and helpful but I learnt a lot when eventually steered to the simes link and the angusj link where many of the various solving techniques are clearly described for those unfamiliar with them.

I was unsure as to whether this post should be in the "General" section as a new topic but decided here as it hopefully will complement Ruud's and em's above posts. Good luck elmerfudd with your puzzle solving.

Cec

[elmerfudd56]

Em,

Thanks for your further explanation of the coloring technique. I have been doing Sudoku puzzles for about a month now, they're very addicting. I managed to figure out the simpler elimination techniques on my own, but could never solve the more difficult puzzles. I knew I must be missing something so I went searching on-line and found this forum and discovered the more advanced techniques ( x-wing, hidden/naked trips/quads etc). I basically understand them but I am still having trouble finding them in the puzzle.

This is a very helpful forum. Kudos to everyone involved.