Puzzle I partly solved, then got totally stuck... help!

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Puzzle I partly solved, then got totally stuck... help!

Postby spamanon » Wed Dec 03, 2008 5:18 pm

This was listed as easy, but I beg to differ. I have read all of the techniques on sudoku dragon, but I don't see how any of them apply except the guess and check (labyrinth). Please tell me I am missing something so that I don't have to guess and check! Here is the puzzle as it now stands:

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


I would appreciate it if someone could show me how to deduce logically any next step. Thanks!

Here is the original, so you can see I have done some work:


Code: Select all
2 . 6 | . 7 . | 3 . 8
4 . . | . . . | . . 9
. 1 . | 3 . 4 | . 6 .
------+-------+-----
. 2 . | 7 . 9 | . 3 .
. . . | . . . | . . .
. 3 . | 5 . 8 | . 9 .
------+-------+-----
. 4 . | 2 . 6 | . 8 .
1 . . | . . . | . . 7
3 . 9 | . 5 . | 1 . 4
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Postby Luke » Wed Dec 03, 2008 7:13 pm

Hi, spamanon. Really enjoyable puzzle. You mentioned it was listed as "easy" but it's a step above that. With pencil marks your progress probably looks like this:
Code: Select all
 
 *-----------------------------------------------------------*
 | 2     59    6     | 19    7     15    | 3     4     8     |
 | 4     7     3     | 6     8    *25    |*25    1     9     |
 | 589   1     58    | 3    *29    4     | 7     6     25    |
 |-------------------+-------------------+-------------------|
 | 568   2     1458  | 7     46    9     | 458   3     156   |
 | 5689  59    458   | 14    3    12     | 2458  7     256   |
 | 67    3     147   | 5    *246   8     |-24    9     126   |
 |-------------------+-------------------+-------------------|
 | 57    4     57    | 2     1     6     | 9     8     3     |
 | 1     8     2     | 49    49    3     | 6     5     7     |
 | 3     6     9     | 8     5     7     | 1     2     4     |
 *-----------------------------------------------------------*
There are several singles chains like this that will help. They stand out if you "filter" the candidates. Then with all the bivalue cells there will be a few XY chains to move things along.

If you're interested in fish, a finned xwing accomplishes the same elimination shown above. (xwing = r2c67 and r5c67, fin = r5c9.) That opens up an xwing on 2 (r3c59 and r6c59; r5c9<>2.)
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Postby spamanon » Thu Dec 04, 2008 6:08 am

There are several singles chains like this that will help. They stand out if you "filter" the candidates. Then with all the bivalue cells there will be a few XY chains to move things along.

If you're interested in fish, a finned xwing accomplishes the same elimination shown above. (xwing = r2c67 and r5c67, fin = r5c9.) That opens up an xwing on 2 (r3c59 and r6c59; r5c9<>2.)


Thanks for your help, but I don't quite understand the terminology you are using. Where is a good source to find out what a chain, a filter, XY chains are? I do know about the xwings from sudokudragon.


Thanks.
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Postby Pat » Thu Dec 04, 2008 6:24 am

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