The New Sudoku Players' Forum

[Gee]

I have read just about everything there is on the subject of forcing chains but this puzzle has me stumped.

I am afriad to use any notation but I can tell you the cells and the values I assigned to each.

Hopefully, someone can help me.

The forcing chain in question is:

r5c2=2 r5c3=8 r5c9=9 r4c8 r4c4=9 r4c2=7

I thought since the beginning call was a 2 and the ending cell was a 7 there was no conflict and that r5c2 should equal 2....not so. what is the error of my thinking???

*-----------*
|..4|...|..6|
|.3.|.5.|4..|
|..7|.21|..3|
|---+---+---|
|..3|..6|..4|
|...|...|...|
|9..|8..|7..|
|---+---+---|
|3..|27.|9..|
|..1|.9.|.4.|
|7..|...|8..|
*-----------*


*-----------*
|..4|38.|1.6|
|13.|65.|4..|
|..7|421|5.3|
|---+---+---|
|..3|.16|2.4|
|4..|.35|61.|
|916|842|735|
|---+---+---|
|385|274|961|
|..1|598|347|
|749|163|852|
*-----------*


*--------------------------------------------------*
| 25 259 4 | 3 8 79 | 1 27 6 |
| 1 3 28 | 6 5 79 | 4 27 89 |
| 68 69 7 | 4 2 1 | 5 89 3 |
|----------------+----------------+----------------|
| 58 57 3 | 79 1 6 | 2 89 4 |
| 4 27 28 | 79 3 5 | 6 1 89 |
| 9 1 6 | 8 4 2 | 7 3 5 |
|----------------+----------------+----------------|
| 3 8 5 | 2 7 4 | 9 6 1 |
| 26 26 1 | 5 9 8 | 3 4 7 |
| 7 4 9 | 1 6 3 | 8 5 2 |
*--------------------------------------------------*

[Pat]

I have read just about everything there is on the subject of forcing chains
but this puzzle has me stumped.

The forcing chain in question is:
r5c2=2 r5c3=8 r5c9=9 r4c4=9 r4c2=7
I thought since the beginning call was a 2 and the ending cell was a 7 there was no conflict and that r5c2 should equal 2....not so. what is the error of my thinking???

Code: Select all

 *-----------*
 |..4|...|..6|
 |.3.|.5.|4..|
 |..7|.21|..3|
 |---+---+---|
 |..3|..6|..4|
 |...|...|...|
 |9..|8..|7..|
 |---+---+---|
 |3..|27.|9..|
 |..1|.9.|.4.|
 |7..|...|8..|
 *-----------*


 *-----------*
 |..4|38.|1.6|
 |13.|65.|4..|
 |..7|421|5.3|
 |---+---+---|
 |..3|.16|2.4|
 |4..|.35|61.|
 |916|842|735|
 |---+---+---|
 |385|274|961|
 |..1|598|347|
 |749|163|852|
 *-----------*

 
 *--------------------------------------------------*
 | 25   259  4    | 3    8    79   | 1    27   6    |
 | 1    3    28   | 6    5    79   | 4    27   89   |
 | 68   69   7    | 4    2    1    | 5    89   3    |
 |----------------+----------------+----------------|
 | 58   57   3    | 79   1    6    | 2    89   4    |
 | 4    27   28   | 79   3    5    | 6    1    89   |
 | 9    1    6    | 8    4    2    | 7    3    5    |
 |----------------+----------------+----------------|
 | 3    8    5    | 2    7    4    | 9    6    1    |
 | 26   26   1    | 5    9    8    | 3    4    7    |
 | 7    4    9    | 1    6    3    | 8    5    2    |
 *--------------------------------------------------*



yes, there is no conflict in this chain

therefore, r5c2 could equal 2
( as far as this chain is concerned )

"could" does not prove "should"

[Gee]

I guess I was under the false impression that if the beginning and ends of the chain terminated, in this case block 4, and there were no conflicts that r5c2=2 would be correct. Back to the drawing board!

[ArkieTech]

Gee,

There is an xy wing that will solve the puzzle.

dan

[Gee]

Thanks Dan. I missed that in my quest to find a forcing chain. Forcing chains have been a problem and I guess I will have to work on it although I though I had it down "pat".

[wintder]

To me, forcing chains are last hope.

This is an easy puzzle.

Code: Select all


Easy stuff to an xy wing.  Pretty much done.

.---------------.---------------.---------------.
|*25   259  4   | 3    8    79  | 1    27   6   |
| 1    3   *28  | 6    5    79  | 4    27   89  |
| 68   69   7   | 4    2    1   | 5    89   3   |
:---------------+---------------+---------------:
|*58   57   3   | 79   1    6   | 2    89   4   |
| 4    27   2-8 | 79   3    5   | 6    1    89  |
| 9    1    6   | 8    4    2   | 7    3    5   |
:---------------+---------------+---------------:
| 3    8    5   | 2    7    4   | 9    6    1   |
| 26   26   1   | 5    9    8   | 3    4    7   |
| 7    4    9   | 1    6    3   | 8    5    2   |
'---------------'---------------'---------------'

If you prefer bugs,  use them!

.---------------.---------------.---------------.
| 25   59-2 4   | 3    8    79  | 1    27   6   |
| 1    3    28  | 6    5    79  | 4    27   89  |
| 68   69   7   | 4    2    1   | 5    89   3   |
:---------------+---------------+---------------:
| 58   57   3   | 79   1    6   | 2    89   4   |
| 4    27   28  | 79   3    5   | 6    1    89  |
| 9    1    6   | 8    4    2   | 7    3    5   |
:---------------+---------------+---------------:
| 3    8    5   | 2    7    4   | 9    6    1   |
| 26   26   1   | 5    9    8   | 3    4    7   |
| 7    4    9   | 1    6    3   | 8    5    2   |
'---------------'---------------'---------------'

[Gee]

Hi Winter....Yeah, forcing chain have been the hardest of the Sudoku solving techniques for me to learn. In fact, I am still at it. Thanks for your reply.

Glenn