Basic solving explanation.

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Basic solving explanation.

Postby moyk » Tue Sep 03, 2013 2:52 pm

Hi,

Attached is the sudoku i'm dealing with.
I just want to make sure if it's accurate to say that we can get rid of the 1 in r7c1 and r7c3, based on the rectangle r5c1 r5c3 r7c1 r7c3. Is that positive?

Is that a UR?

Thanks in advance for your help.
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Re: Basic solving explanation.

Postby JasonLion » Wed Sep 04, 2013 12:34 pm

Almost, but wrong elimination digit/location. If neither R7C1 or R7C3 could be 5 you would have a deadly pattern on 1 and 6. Thus, one of those two cells must be 5. Because of that you can eliminate all of the other 5s in R7 and B7.
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Re: Basic solving explanation.

Postby eleven » Sat Sep 07, 2013 11:58 am

moyk wrote:I just want to make sure if it's accurate to say that we can get rid of the 1 in r7c1 and r7c3, based on the rectangle r5c1 r5c3 r7c1 r7c3. Is that positive?

Yes. Because of the strong link for 6 in row 7.

Note, that no solution with digits
Code: Select all
a . b |
--------
b . a |

in UR cells (the 4 cells being in 2 rows, 2 columns and 2 boxes) can be unique, if none of the 4 digits was given.
So any candidate, which forces such a pattern, can be eliminated.

If you have no 5 in r7c13, either 1661 or 6116 is forced. So one of the 2 cells must be 5.
If you have a 1 in r7c1, then r7c3=6, r5c3=1 and r5c1=6 - deadly.
Same for r7c3=1: -> r7c1=6, r5c1=1, r5c3=6.
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