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chicago tribune 1/19/18

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mtharp

Joined: 19 Jun 2006
Posts: 30

Posted: Sat Jan 20, 2018 2:28 am Post subject: chicago tribune 1/19/18

Again, dailysudoku graded this one as too hard and I got stuck (again):

Code:

+--------------+---------------+--------------+
| 1567 9 157 | 4 157 2 | 8 156 3 |
| 8 4 157 | 1367 9 357 | 2 156 15 |
| 156 3 2 | 16 15 8 | 9 7 4 |
+--------------+---------------+--------------+
| 479 15 8 | 237 6 3457 | 135 1459 27 |
| 2 6 347 | 9 457 1 | 35 45 8 |
| 479 15 3479 | 237 8 3457 | 6 1459 27 |
+--------------+---------------+--------------+
| 3 7 59 | 8 14 6 | 145 2 159 |
| 59 2 6 | 17 3 47 | 145 8 159 |
| 14 8 14 | 5 2 9 | 7 3 6 |
+--------------+---------------+--------------+

Play this puzzle online at the Daily Sudoku site

Any logic or pattern help appreciated.

Keith, I have not yet tried your strong links mapping technique, but will attempt to do so.

Mike

ZeroAssoluto

Joined: 05 Feb 2017
Posts: 942
Location: Rimini, Italy

Posted: Sat Jan 20, 2018 8:31 am Post subject:

Hi everyone,

Code:

Play this puzzle online at the Daily Sudoku site

UR with 2,7 in r46c49 and -3 in r2c4,r46c6

after same basic

Code:

+--------------+-------------+-------------+
| 1567 9 157 | 4 157 2 | 8 156 3 |
| 8 4 157 | 167 9 3 | 2 156 15 |
| 156 3 2 | 16 15 8 | 9 7 4 |
+--------------+-------------+-------------+
| 479 15 8 | 23 6 457 | 13 149 27 |
| 2 6 347 | 9 47 1 | 35 45 8 |
| 479 15 3479 | 23 8 457 | 6 149 27 |
+--------------+-------------+-------------+
| 3 7 59 | 8 14 6 | 145 2 159 |
| 59 2 6 | 17 3 47 | 145 8 159 |
| 14 8 14 | 5 2 9 | 7 3 6 |
+--------------+-------------+-------------+

Play this puzzle online at the Daily Sudoku site

Skyscraper with number 7 in r2c34,r5c35 and -7 in r1c5

Code:

+------------+----------+------------+
| 6 9 7 | 4 15 2 | 8 15 3 |
| 8 4 15 | 7 9 3 | 2 6 15 |
| 15 3 2 | 6 15 8 | 9 7 4 |
+------------+----------+------------+
| 479 15 8 | 23 6 45 | 13 149 27 |
| 2 6 34 | 9 7 1 | 35 45 8 |
| 479 15 349 | 23 8 45 | 6 149 27 |
+------------+----------+------------+
| 3 7 59 | 8 4 6 | 15 2 159 |
| 59 2 6 | 1 3 7 | 4 8 59 |
| 14 8 14 | 5 2 9 | 7 3 6 |
+------------+----------+------------+

Play this puzzle online at the Daily Sudoku site

Skyscraper with number 5 in r2c39,r8c19 and -5 in r3c1,r7c3

and everything is easy until the end

Ciao Gianni

mtharp

Joined: 19 Jun 2006
Posts: 30

Posted: Sun Jan 21, 2018 12:53 am Post subject:

Gianni, thank you. I follow the logic but will have to look up why the pattern is called skyscraper. Mike

Marty R.

Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

Posted: Mon Jan 22, 2018 12:27 am Post subject:

Quote:

I follow the logic but will have to look up why the pattern is called skyscraper.

This is from a classic post by Havard.

Of course, the name comes from when the two strong links are in columns.

"This pattern is part of the Turbot Fish, and I have named it a "skyscraper" because of the way the two strong links looks a bit like two skyscrapers to me.."

Ajò Dimonios

Joined: 01 May 2017
Posts: 339
Location: Sassari Italy

Posted: Sat Jan 27, 2018 2:26 pm Post subject:

Hi everyone Solution in one step using " La technique des pistes de Robert Mauriès". The track created by inserting 5 in R2C9 is invalid because using only the basic technique creates a contradiction. In this way, by eliminating 5 in R2C9, the solution is easily reached and the uniqueness is demonstrated. Ciao a Tutti Paolo

keith

Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

Posted: Tue Jan 30, 2018 3:22 pm Post subject:

Quote:

Keith, I have not yet tried your strong links mapping technique, but will attempt to do so.

I'll make this into a tutorial later today.

Keith

dongrave

Joined: 06 Mar 2014
Posts: 568

Posted: Tue Jan 30, 2018 9:58 pm Post subject:

keith wrote:

Quote:

Keith, I have not yet tried your strong links mapping technique, but will attempt to do so.

I'll make this into a tutorial later today.

Keith

Hi Keith! Please post a link here if you can to your tutorial when you've finished! I'd love to check it out! Thanks, Don.

keith

Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

Posted: Tue Jan 30, 2018 11:03 pm Post subject:

The following is my attempt at a recipe. It is not 100% accurate, but it is good enough for almost all the puzzles you will see.
A Sudoku puzzle looks like this:

Code:

   |    |   
   |    |   
   |    |   
-------+--------+-------
   |    |   
   |    |   
   |    |   
-------+--------+-------
   |    |   
   |    |   
   |    |   

There are 81 cells in 9 rows, 9 columns, and 9 3x3 boxes. Rows and columns together are called “lines”. Lines and boxes together are called “houses”.
You should learn to quickly draw such a diagram (an empty Tic-Tac-Toe grid) in the margin of a puzzle you are solving.
Now, we are talking here only about solving a single unknown digit. This will not help you find XY- or XYZ-wings, which are multi-digit patterns.
Examples of single-digit patterns are X-wings and all the rest of the fish (swordfish, etc.) and Turbots, which include skyscrapers and kites.
There are three things you need to know:
1. Strong Links
A strong link in a single digit means that digit can only occur in two cells in a house. The logic is, one cell is not true, and the other is true. You should sit down and contemplate this idea. It is extremely important.
2. Strong links can line up
Strong links often align at two starting cells. The logic is, at least one of these is not true. At the other end of the links, the logic then is, at least one of these is true. So, the ending cells are “pincers”.
3. Only certain boxes are useful
This is, I think, a profound insight for those of us who solve puzzles with pencil and paper. It took me 20 years to realize, so I don’t expect you to immediately say, “Oh yes, of course”.
If you look at the 9 cells in a box, an unknown digit may occur only in a line (a row or column), or it may occur in both, like this example:

Code:

 

 

I have (unfortunately) in the past called this a Type C box.
The insight is, a useful strong link must both start and end in a Type C box. (This is the part that is not 100% accurate.)
The corollary to this statement is that for a strong link elimination to be possible, there must be four Type C boxes in a rectangle, like this:

Code:

C C

C C

So, how does this work? Here is the posted puzzle:

Code:

1567 9 157 | 4 157 2 | 8 156 3
8 4 157 | 1367 9 357 | 2 156 15
156 3 2 | 16 15 8 | 9 7 4
-------------+---------------+-------------
479 15 8 | 237 6 3457 | 135 1459 27
2 6 347 | 9 457 1 | 35 45 8
479 15 3479 | 237 8 3457 | 6 1459 27
-------------+---------------+-------------
3 7 59 | 8 14 6 | 145 2 159
59 2 6 | 17 3 47 | 145 8 159
14 8 14 | 5 2 9 | 7 3 6

Let’s ignore the Unique Rectangle and the XYZ-wing, and look at the single-digit patterns.
For 1, 3, 4, 6, 8, and 9 there are no possibilities. Look especially at digit 4. There are not four Type C boxes in a rectangle. Move on. You could otherwise waste a lot of time here.

For 2 and 5, I do not see any eliminations, but look at 7:

Code:

  |  |
 |   |
| |
-----+------+-------
 |   | 
 |  |
  |   | 
-----+------+-------
| |
|   |
| |

Boxes 1, 2, 4 and 5 are Type C. They lie in a rectangle.
At least 1 of R1C1 and R1C4 is not 7. So, at least one of (R4C1 or R6C1) or R5C5 is 7. So, R5C3 cannot be 7. This is called a “grouped skyscraper”.
A few more basics get us here:

Code:

+-------------+-------------+-------------+
| 6 9 7 | 4 15 2 | 8 15 3 |
| 8 4 15 | 7 9 3 | 2 6 15 |
| 15 3 2 | 6 15 8 | 9 7 4 |
+-------------+-------------+-------------+
| 479 15 8 | 23 6 45 | 13 149 27 |
| 2 6 34 | 9 7 1 | 35 45 8 |
| 479 15 349 | 23 8 45 | 6 149 27 |
+-------------+-------------+-------------+
| 3 7 59 | 8 4 6 | 15 2 159 |
| 59 2 6 | 1 3 7 | 4 8 59 |
| 14 8 14 | 5 2 9 | 7 3 6 |
+-------------+-------------+-------------+

Boxes 1,3,7, and 9 are type C for digit 5, and there are a number of kites and skyscrapers to eliminate a 5 and solve the puzzle.

Keith

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