The New Sudoku Players' Forum

[skjalg]

Hi.

I am new to the forum, and while I am quite familiar with the Simple Sudoku Technique Set, I have not previosly ventured into the more complicated puzzles. However this time I have, but I am stuck.

So far, but not further:

Code: Select all

*---+---+---*
|49.|.8.|31.|
|583|.1.|6..|
|2.1|.43|9.8|
|---+---+---|
|.2.|...|48.|
|3.4|298|.61|
|1.8|4..|293|
|---+---+---|
|.4.|82.|.36|
|612|..4|8.9|
|83.|..6|...|
*---+---+---*

*------------+------------+------------*
| 4   9   67 | 567 8   257| 3   1   257|
| 5   8   3  | 79  1   279| 6   24  247|
| 2   67  1  | 567 4   3  | 9   57  8  |
|------------+------------+------------|
| 79  2   679| 137 356 157| 4   8   57 |
| 3   57  4  | 2   9   8  | 57  6   1  |
| 1   567 8  | 4   567 57 | 2   9   3  |
|------------+------------+------------|
| 79  4   579| 8   2   19 | 15  3   6  |
| 6   1   2  | 357 357 4  | 8   57  9  |
| 8   3   59 | 19  57  6  | 157 24  24 |
*------------+------------+------------*


Could anyone point out to me how to proceed (technique used - if possible a description, or cross link to the description.)

Thanks in advance.

Skjalg

[storm_norm]

Skjalg,

nice puzzle... this puzzle is full of useful, visual patterns and if you haven't already, I would take notes on remote pairs and Uniquie Rectangles which are very useful visually and can be spotted easily.

along that same path is the W-wing and the M-wing which take a little more understand but can also be spotted easily.

Code: Select all

.------------------.------------------.------------------.
| 4     9     67   | 567   8     257  | 3     1     257  |
| 5     8     3    | 79    1     279  | 6    #24   #247  |
| 2     67    1    | 567   4     3    | 9     57    8    |
:------------------+------------------+------------------:
| 79    2     679  | 1357  3567  157  | 4     8     57   |
| 3     57    4    | 2     9     8    | 57    6     1    |
| 1     567   8    | 4     567   57   | 2     9     3    |
:------------------+------------------+------------------:
| 79    4     579  | 8     2     19   | 157   3     6    |
| 6     1     2    | 357   357   4    | 8     57    9    |
| 8     3     579  | 19    57    6    | 157  #24   #24   |
'------------------'------------------'------------------'

don't know if I can cross link it but I hope you notice in r29c89
take a look at the {2,4} candidates
this is a Unique Rectangle type 1. this type allows you to eliminate 2 and 4 from r2c9.

the rule states that if all four cells in the rectangle contain only the digits 2 and 4, then the puzzle will not have a unique solution (hence the name of the technique) because you will be able to switch the 2 and the 4 in any cell and end up with another solution, which is a no no.

so with this in mind, you will notice that three of the four corners of the rectangle have only two candidates {2,4} except r2c9... in order to avoid the Deadly Pattern of having more than one solution you can safely eliminate the 2 and 4 from r2c9.
also. this rectangle can only happen in two boxes.

that will get you going for a while.

later on you will see a commonly used coloring technique. the candidate 7 will present it nicely.

this isn't the only path you can take... I presented the uniqueness test path because I know the non-uniqueness crowd will have thier say. but I argue this is the prettiest

[skjalg]

Thanks for the prompt and useful feedback.

The Unique Rectangle type 1 was what I needed to complete the puzzle, along with the Alternating Colours with 7 that you referred to. I agree that this was visually easy to spot, once the technique was pointed out.

I will investigate the W-wing and the M-wing as well as remote pairs, as I have not used those previously.

I have a few other puzzles that stopped me in the past, I might post a few of them later, once I investigate these (to me) new techniques.

Once again, thank you.

Skjalg

[Glyn]

skjalg Welcome to the forum. storm_norm's UR was the easiest way to go on this one. Interestingly once we assumed uniqueness, we could have skipped the coloring move and noticed the BUG+1 that you get here, giving r1c4=7.

Code: Select all

.------------.------------.------------.
| 4   9   67 | 567 8   57 | 3   1   2  |
| 5   8   3  | 9   1   2  | 6   4   7  |
| 2   67  1  | 67  4   3  | 9   5   8  |
:------------+------------+------------:
| 9   2   67 | 37  36  1  | 4   8   5  |
| 3   5   4  | 2   9   8  | 7   6   1  |
| 1   67  8  | 4   56  57 | 2   9   3  |
:------------+------------+------------:
| 7   4   5  | 8   2   9  | 1   3   6  |
| 6   1   2  | 35  35  4  | 8   7   9  |
| 8   3   9  | 1   7   6  | 5   2   4  |
'------------'------------'------------'

[skjalg]

Glyn,

Thanks for pointing that out. It seems the concept of these Alomost Deadly Patterns is a strong one.

For those interested in the original puzzle, here it is:

Code: Select all

*---+---+---*
|4..|...|...|
|5..|.1.|6..|
|..1|.43|9.8|
|---+---+---|
|.2.|...|48.|
|..4|.9.|...|
|..8|4..|2.3|
|---+---+---|
|...|8..|.36|
|.12|...|..9|
|.3.|..6|...|
*---+---+---*


Regards,

Skjalg