dailysudoku.com

Bill Denholm · Posted: Sun Sep 17, 2006 2:03 am Post subject: Sept 16 - very hard

I got stuck and asked for a hint. The program gave me 5 in R5C9. I found the UR (X-Wing) but I thought that only let me eliminate 1s inside of the rectangle. Is this correct? Otherwise, what is the logic behind the hint?

Bill

David · Joined: 02 Jun 2006 Posts: 58 Location: Bedford, UK

Hi Bill,

Do you mean the hint was row 9 column 5 ?

Marty R. · Posted: Sun Sep 17, 2006 3:53 pm Post subject:

An X-Wing is not the same as a UR. With an X-Wing on columns, you can eliminate the number from all other rows in the two columns, and eliminate from all other columns with an X-Wing on rows.

I did this puzzle with pencil and paper. After the basic moves, there was an X-Wing on "1" in columns and the eliminations therefrom allowed completion of the puzzle with basic techniques.

Here's a good explanation of X-Wings. Scroll down about halfway to find it.

http://www.angusj.com/sudoku/hints.php

Bill Denholm · Posted: Sun Sep 17, 2006 5:28 pm Post subject:

Yes, that was what I meant. <g> I got them xx.

Bill

Bill Denholm · Posted: Sun Sep 17, 2006 5:32 pm Post subject:

Marty,

Thanks. I guess I don't understand the difference between an X-Wing and a Unique Rectangel (UR), if there is one.

Bill