## forcing chains again?

Post the puzzle or solving technique that's causing you trouble and someone will help

### forcing chains again?

Code: Select all
`+-------+-------+-------+| . 5 . | . 8 . | . 7 . | | . 4 . | . . . | 2 . . | | 7 . . | . 9 . | . . 1 | +-------+-------+-------+| 1 . . | . . . | . 2 . | | . . . | 8 7 6 | . . . | | . 3 . | . . . | . . 9 | +-------+-------+-------+| 6 . . | . 3 . | . . 7 | | . . 3 | . . . | . 8 . | | . 2 . | . 5 . | . 6 . | +-------+-------+-------+`

Code: Select all
`+-------------+----------------+--------------+| 239 5  1269 | 12346 8  1234  | 3469 7   346 | | 39  4  1689 | 13567 16 1357  | 2    359 568 | | 7   68 268  | 23456 9  2345  | 3458 35  1   | +-------------+----------------+--------------+| 1   67 5    | 39    4  39    | 678  2   68  | | 24  9  24   | 8     7  6     | 135  135 35  | | 8   3  67   | 15    2  15    | 67   4   9   | +-------------+----------------+--------------+| 6   18 489  | 1249  3  12489 | 1459 159 7   | | 5   17 3    | 14579 16 1479  | 149  8   2   | | 49  2  4789 | 1479  5  14789 | 1349 6   34  | +-------------+----------------+--------------+`

according to the susser solver, i need to use forcing chains for the next step. is there an easier way of recognizing a forcing chain or are there other techniques which can solve it??
mantouq

Posts: 6
Joined: 07 February 2006

Well, first of all, there is only one place for a 6 in row 8.

A bit later, you might need the hint from this thread too.

Vidar
vidarino

Posts: 295
Joined: 02 January 2006

sorry there's an amendment to r8c4. the correct one is here:

Code: Select all
`+-------------+----------------+--------------+| 239 5  1269 | 12346 8  1234  | 3469 7   346 || 39  4  1689 | 13567 16 1357  | 2    359 568 || 7   68 268  | 23456 9  2345  | 3458 35  1   |+-------------+----------------+--------------+| 1   67 5    | 39    4  39    | 678  2   68  || 24  9  24   | 8     7  6     | 135  135 35  || 8   3  67   | 15    2  15    | 67   4   9   |+-------------+----------------+--------------+| 6   18 489  | 1249  3  12489 | 1459 159 7   || 5   17 3    | 14679 16 1479  | 149  8   2   || 49  2  4789 | 1479  5  14789 | 1349 6   34  |+-------------+----------------+--------------+`
mantouq

Posts: 6
Joined: 07 February 2006

mantouq wrote:sorry there's an amendment to r8c4. the correct one is here: ...

Ah. In that case I'll simply refer you to the thread I linked to above.

Vidar
vidarino

Posts: 295
Joined: 02 January 2006

Attempting another approach,

My solver couldn't be solved without chains,

A total of chains & 2 Almost locked cells eliminations were used.

Tarek

tarek

Posts: 2761
Joined: 05 January 2006

Alternatively, this puzzle can be solved in one step with a Single Implication Network. See the thread "Can't force chains on this one??" for further details.

Carcul
Carcul

Posts: 724
Joined: 04 November 2005

My solver cracked it with a few ALS-eliminations! I love that stuff!
Havard

Posts: 377
Joined: 25 December 2005

Hello Havard,

please show me the first ALS!
I am trying to implement ALS in my solver,
but have no strategy, to find them
absolute beginner

Posts: 22
Joined: 26 February 2006

bennys

Posts: 156
Joined: 28 September 2005

absolute beginner wrote:Hello Havard,

please show me the first ALS!
I am trying to implement ALS in my solver,
but have no strategy, to find them

You were just given a link from the very person that thought of this stuff!

Bennys:
I think ALS is one of the greatest discoveries in Sudoku solving! Finally a alternative to forcing chains /loops that cracks the really hard puzzles. Kudos to you!
Havard

Posts: 377
Joined: 25 December 2005

Benny,
thank You very much.
I thought, xyz-wings were difficult to implement ;-),
but ALS will really be challenging.

( and, yes, i did know, what bipartite graphs are )
but I think, thats nice for implementing a solver,
but not very good for paper&pencil.
And if you are really interested in a solution,
use a backtracking-alg and the work is done.
Thats not the chanllenge
absolute beginner

Posts: 22
Joined: 26 February 2006

Thanks
bennys

Posts: 156
Joined: 28 September 2005