## Superior Sudoku 21

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### Superior Sudoku 21

Does anyone have any idea how to solve this? If so, may you explain swordfish or x-wing techniques used?

Thanks!
TheSavage4

Posts: 4
Joined: 18 December 2005

did you get the naked quads in box 1? (4 cells that together contain only 4 numbers, so those 4 numbers MUST go in those cells - you can therefore eliminate them from other cells in that box).

Code: Select all
` *-----------* |...|...|.18| |..8|491|.2.| |..1|.38|...| |---+---+---| |.4.|...|8.2| |63.|...|741| |8.7|..4|.9.| |---+---+---| |...|64.|5..| |.9.|.23|1..| |...|...|2..| *-----------*  *--------------------------------------------------------------------* | 34579  257    3459   | 257    567    2567   | 49     1      8      | | 57     567    8      | 4      9      1      | 36     2      3567   | | 24579  2567   1      | 257    3      8      | 49     567    567    | |----------------------+----------------------+----------------------| | 159    4      59     | 13579  1567   5679   | 8      356    2      | | 6      3      259    | 2589   58     259    | 7      4      1      | | 8      125    7      | 1235   156    4      | 36     9      356    | |----------------------+----------------------+----------------------| | 1237   1278   23     | 6      4      79     | 5      378    379    | | 457    9      456    | 578    2      3      | 1      678    467    | | 13457  1578   3456   | 15789  1578   579    | 2      3678   34679  | *--------------------------------------------------------------------*`
Shazbot

Posts: 220
Joined: 24 September 2005

Looking back, I noticed the 349 in box 1 instead ( ie not in c2 or r2) but I cannot for the life of me work out how I excluded a 3 from r2c1, although I can see from my simple pencil marks that I did.
Bigtone53

Posts: 413
Joined: 19 September 2005

Getting the quad and triple in box 1 was the key to this puzzle. It was fairly straightforward after that. No x-wings or swordfish required.
CathyW

Posts: 316
Joined: 20 June 2005

I cannot for the life of me work out how I excluded a 3 from r2c1

OK remembered. To do with certain numbers in box 3.
Bigtone53

Posts: 413
Joined: 19 September 2005

yes - in box 3, candidate 3s are "locked" to the middle row, so 3s can be removed from the rest of row 2. And you're doing well to spot the 349 - called a hidden triple - I struggle with ANYTHING hidden!
Shazbot

Posts: 220
Joined: 24 September 2005

As Cathy W said - fairly straightforward. Definitely no swordfish, because I just don't understand them (I have seen the online guides, and each time I read them, I think I understand and then when I use them I get it wrong. So clearly I didn't understand). The majority (say, 90%) of superiors I have done, I have been able to do - but whenever I try and use a swordfish - utter disaster.
dalek

Posts: 17
Joined: 28 September 2005

And you're doing well to spot the 349 - called a hidden triple - I struggle with ANYTHING hidden!

So would I, if I pencilled in all the candidates. Instead I looked at column 2 and row 2 and saw that they both have 349 elsewhere than in box 1. This eliminates every square but 3 for these numbers in box 1.
Bigtone53

Posts: 413
Joined: 19 September 2005

### Sudoku 21

In the quote, below, why is 2 not part of the candidate moves in the first box? Also, may you please specify WHAT four numbers are in common?

I am new to this sudoku lingo. When you say Box 1, does that mean the one on the top left corner?

Thanks.

Shazbot wrote:did you get the naked quads in box 1? (4 cells that together contain only 4 numbers, so those 4 numbers MUST go in those cells - you can therefore eliminate them from other cells in that box).

Code: Select all
` *-----------* |...|...|.18| |..8|491|.2.| |..1|.38|...| |---+---+---| |.4.|...|8.2| |63.|...|741| |8.7|..4|.9.| |---+---+---| |...|64.|5..| |.9.|.23|1..| |...|...|2..| *-----------*  *--------------------------------------------------------------------* | 34579  257    3459   | 257    567    2567   | 49     1      8      | | 57     567    8      | 4      9      1      | 36     2      3567   | | 24579  2567   1      | 257    3      8      | 49     567    567    | |----------------------+----------------------+----------------------| | 159    4      59     | 13579  1567   5679   | 8      356    2      | | 6      3      259    | 2589   58     259    | 7      4      1      | | 8      125    7      | 1235   156    4      | 36     9      356    | |----------------------+----------------------+----------------------| | 1237   1278   23     | 6      4      79     | 5      378    379    | | 457    9      456    | 578    2      3      | 1      678    467    | | 13457  1578   3456   | 15789  1578   579    | 2      3678   34679  | *--------------------------------------------------------------------*`
TheSavage4

Posts: 4
Joined: 18 December 2005

I don't know but it doesn't matter the naked quad is still valid. If there should have been a 2 candidate in cell 1 then it can be erased by the naked quad
Pi

Posts: 389
Joined: 27 May 2005

When you say Box 1, does that mean the one on the top left corner?

I cannot help you with your particular question, as I do not solve by pencilling all candidates but yes, convention is to label the 9x9 boxes 1 to 9, left to right from top left to bottom right. Particular cells (single number squares) are labelled by row and column in that order ie r4c7 = the cell at row 4 (from the top) column 7 (from the left).
Bigtone53

Posts: 413
Joined: 19 September 2005

Pi

Posts: 389
Joined: 27 May 2005

Perhaps, in some day in some week in some month of some year in the wild blue yonder, someone will get around to answering WHAT FOUR NUMBERS IN WHAT CELLS need to be eliminated in box 1 to satisfy the naked quad.

Thanks!

Pi wrote:I don't know but it doesn't matter the naked quad is still valid. If there should have been a 2 candidate in cell 1 then it can be erased by the naked quad
TheSavage4

Posts: 4
Joined: 18 December 2005

The blue cells form the naked quad. This means that the 2 5 6 and 7 must be in those blue cells. Therefore, you can remove all candidate 2 5 6 and 7 from the yellow squares.
Lardarse

Posts: 106
Joined: 01 July 2005

Thanks. However, on c1r2, how did you manage to get rid of the candidate 3? Does that make a difference?

Lardarse wrote:
The blue cells form the naked quad. This means that the 2 5 6 and 7 must be in those blue cells. Therefore, you can remove all candidate 2 5 6 and 7 from the yellow squares.
TheSavage4

Posts: 4
Joined: 18 December 2005

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