The New Sudoku Players' Forum

[Kent]

need help with this.Can we use colour coding or swordfish here??

Code: Select all

 *--------------------------------------------------*
 | .    .    7    | 6    4    1    | 8    .    5    |
 |5    .     .    | 2    8    3    | .    .    7    |
 | .    8    .    | 7    5    9    | .    2    . |
 |----------------+----------------+----------------|
 | 6   1   5   |   4    9    8   | 2    7    3   |
 | 8   4   3   l   5    7    2   | 9    6     1  |
 | 9   7   2   |   1   3     6   | 5    4     8   |
 |----------------+----------------+----------------|
 | .    5   .    |  3    2    7   | .    8   9   |
 | 7   .     8   |  9    1    4   | .    5    .    |
 | .   .    9    |  8    6    5   | 7   .    .    |
 *--------------------------------------------------*

[tarek]

hi Kent,

Advanced techniques I'm afraid, although not that advanced.....

Code: Select all

*--------------------------------------------------------*
|*23   -239   7    | 6     4     1    | 8    *39    5    |
| 5     69    146  | 2     8     3    | 146   19    7    |
|#134   8     146  | 7     5     9    | 1346  2     46   |
|------------------+------------------+------------------|
| 6     1     5    | 4     9     8    | 2     7     3    |
| 8     4     3    | 5     7     2    | 9     6     1    |
| 9     7     2    | 1     3     6    | 5     4     8    |
|------------------+------------------+------------------|
| 14    5     146  | 3     2     7    | 146   8     9    |
| 7     236   8    | 9     1     4    | 36    5     26   |
|*1234  23    9    | 8     6     5    | 7    *13    24   |
*--------------------------------------------------------*
Eliminating 3 From r1c2 (Finned XWing in Columns 18)
*--------------------------------------------------------*
| 23   *29    7    | 6     4     1    | 8    *39    5    |
| 5     69    146  | 2     8     3    | 146   19    7    |
| 134   8     146  | 7     5     9    | 1346  2     46   |
|------------------+------------------+------------------|
| 6     1     5    | 4     9     8    | 2     7     3    |
| 8     4     3    | 5     7     2    | 9     6     1    |
| 9     7     2    | 1     3     6    | 5     4     8    |
|------------------+------------------+------------------|
| 14    5     146  | 3     2     7    | 146   8     9    |
| 7     236   8    | 9     1     4    | 36    5     26   |
| 1234 *23    9    | 8     6     5    | 7    -13    24   |
*--------------------------------------------------------*
Eliminating 3 From r9c8 (9 & 2 in r1c2 form an XY wing with 3 in r1c8 & r9c2)

I couldn't tell exactly wher you've reached in your solution, the first step however is the first non single step if full pencilmarks filled the blanks

Tarek

[Kent]

|*23 -239 7 | 6 4 1 | 8 *39 5 |
| 5 69 146 | 2 8 3 | 146 19 7 |
|#134 8 146 | 7 5 9 | 1346 2 46 |
|------------------+------------------+------------------|
| 6 1 5 | 4 9 8 | 2 7 3 |
| 8 4 3 | 5 7 2 | 9 6 1 |
| 9 7 2 | 1 3 6 | 5 4 8 |
|------------------+------------------+------------------|
| 14 5 146 | 3 2 7 | 146 8 9 |
| 7 236 8 | 9 1 4 | 36 5 26 |
|*1234 23 9 | 8 6 5 | 7 *13 24 |
*--------------------------------------------------------*
Eliminating 3 From r1c2 (Finned XWing in Columns 18)

So where's the fin in this puzzle?? Can r1c2 , r9c2,r1c8 & r9c8 form an x-wing instead of the x wing u gave??

[tarek]

So where's the fin in this puzzle?? Can r1c2 , r9c2,r1c8 & r9c8 form an x-wing instead of the x wing u gave??

The x-wing is basically a group of similar candidtaes occupying 4 cells in a 2 columns- 2 rows formation......... The other cells in the rows mentioned must be candidate free to achieve candidate elimination in other cells in the columns....... or swap it around: The other cells in the columns mentioned must be candidate free to achieve candidate elimination in other cells in the rows.

In finned x-wings we go a step further: it is just your normal x-wing but with extra fin(s) (cells with that candidate) preventing it from being your normal x-wing. in these cases only the candidates in the line of elimination that can "see" the fin(s) can be eliminated.

In the example, if r3c1 didn't have a 3 then we would have your normal x-wing (r19c18) with no other 3s in columns 1 & 8 so possibly eliminating 3s in rows 1 & 9 (eg. r1c2, r9c2).....
However because of this 3 (fin) in r3c1, we can only eliminate the 3 in r1c2 because it can see the fin......

the examples you mentioned are not x-wings nor finned x-wings for the reasons mentioned above.

This an advanced technique, the puzzle above can be solved also with colouring, feel free to use what you think easier to spot.
Tarek

[Kent]

I still don't quite get it.why cant i do x-wing like below.I'ts just quite the same as what u showed me.There's theree '3' in column 1 and 2, so there shoul be no problem having the x wing with candidates from column 1 or 2.

how would the colouring be like in this puzzle?

Code: Select all

 *--------------------------------------------------------*
|23   *239   7    | 6     4     1    | 8    *39    5    |
| 5     69    146  | 2     8     3    | 146   19    7    |
|134   8     146  | 7     5     9    | 1346  2     46   |
|------------------+------------------+------------------|
| 6     1     5    | 4     9     8    | 2     7     3    |
| 8     4     3    | 5     7     2    | 9     6     1    |
| 9     7     2    | 1     3     6    | 5     4     8    |
|------------------+------------------+------------------|
| 14    5     146  | 3     2     7    | 146   8     9    |
| 7    -236   8    | 9     1     4    | 36    5     26   |
|#1234 * 23    9    | 8     6     5    | 7    *13    24   |
*--------------------------------------------------------*

[tarek]

[Edited as the previous reply had mistakes]

Well spotted Kent....

However you can't have the finned x-wing with r9c1 as a fin as removing the fin would not result in an x-wing that eliminates in columns.....There is still the 3 in r1c1....

Tarek

[Kent]

Thanks Tarek. That means there's 2 fin X-wing and we can eliminate 2 candidates with those 2 X-wing???
Why can't r9c1 become a fin???

[tarek]

Why can't r9c1 become a fin???

U just used it as a fin, when u eliminated the 3 in r8c2 however that 3 which you eliminated is also a fin for the 2nd finned x-wing which eliminate the 3 in r9c1 (the fin in the first finned x-wing), you can easily miss one if you've done the other.

Tarek

[Kent]

So as a summary which fin is for which X-wing?? I'm a bit blur here. Can u also tell me how do u complete it with colouring? Thanks

[tarek]

I myself do not like colouring but here is how to eliminate the 3 in r9c1 & r1c2 using simple colouring, achieving what the valid finned x-wings did

Code: Select all

*--------------------------------------------------------*
| 23   -239   7    | 6     4     1    | 8    A39    5    |
| 5     69    146  | 2     8     3    | 146   19    7    |
|A134   8     146  | 7     5     9    |a1346  2     46   |
|------------------+------------------+------------------|
| 6     1     5    | 4     9     8    | 2     7     3    |
| 8     4     3    | 5     7     2    | 9     6     1    |
| 9     7     2    | 1     3     6    | 5     4     8    |
|------------------+------------------+------------------|
| 14    5     146  | 3     2     7    | 146   8     9    |
| 7    a236   8    | 9     1     4    |A36    5     26   |
|-1234  23    9    | 8     6     5    | 7    a13    24   |
*--------------------------------------------------------*

r3c1=3  => r1c2<>3
        => r9c1<>3

r3c1<>3 => r3c7=3 => r8c7<>3 => r8c2=3 => r1c2<>3
        => r3c7=3 => r8c7<>3 => r8c2=3 => r9c1<>3

Therefore r1c2<>3 & r9c1<>3

returning to the finned x-wing.......
if the fin is in rows, you eliminate in columns. When the fin is in columns, you eliminate in rows. Having said that, I made a mistake by saying that your example of a the finned x-wing was correct (I blame the skewed lines in your post as I can't blame myself ), the as you have a 3 in r1c1, then the finned x-wing with the fin in r9c1 is not valid as removing the fin will not result in an x-wing that can eliminate in columns, however the finned x-wing with the fin in r8c2 is fine as removing the fin will result in an x-wing that will eliminate in rows....

Tarek

[Kent]

How do u determine which is the fin if there's 2 candidate.1 at the row and 1 at the column of the x-wing.Is the horizontal or vertical fin??

[tarek]

How do u determine which is the fin if there's 2 candidate.1 at the row and 1 at the column of the x-wing.Is the horizontal or vertical fin??

I've just edited my post above, & will edit some of the posts above, but in answer to your question.......if both finned x-wings are valid, it dowsn't matter which one you choose.

Tarek

[Kent]

So u mean that my X-wing is correct but my fin is qrong.So it should be r8c2 as my fin???
1 more quesion.How do u select the colouring technique? How do u know row or column to start with?? What if i start with r9c1 and procede with the coluring?? Then i wont have to eliminate 3 from r9c1.So it actually depends on where u start right?
[/quote]

[tarek]

So u mean that my X-wing is correct but my fin is qrong.So it should be r8c2 as my fin???

Kent, I think you have to seperate between two things here.....
the x-wing is #1
the finned x-wing is #2

They are different entities...... when you say x-wing then everybody who reads it will understand it as an X-wing (#1), there is no x-wing in the examples above at all.......

the FINNED x-wing(#2) was named this way because it closely resembles the x-wing(#1) as removing the fin(s) from the finned x-wing(#2) will give you the x-wing(#1)....

Mastering the x-wing (#1) as you solve more puzzles will make this easier to grasp as the finned x-wing is a step higher......

Tarek

[Kent]

sorry about the wrong terms what i mean was finned x wing.So regarding my question for the colouring.Can u please explain?? Thanks.