The New Sudoku Players' Forum

[Luke]

Is there such a thing as a rectangle in two boxes containing three strong links that does not have an elimination?

Here's today's (Saturday 6/7/08) "6 Star" fr the San Francisco Chronicle.
(Knight features/Bodycombe)

Code: Select all

 
604109000027000005805600400000700530000591000076008000001003807700000620000907301
+--------------+--------------+--------------+
|    6   3   4 |    1   5   9 |   27  78  28 |
|   19   2   7 |   38  38   4 |   19   6   5 |
|    8  19   5 |    6   7   2 |    4  19   3 |
+--------------+--------------+--------------+
|   12  18   9 |    7  24   6 |    5   3 248 |
|    3   4  28 |    5   9   1 |   27  78   6 |
|    5   7   6 |   23 234   8 |   19 149 249 |
+--------------+--------------+--------------+
|  249  56   1 |   24  26   3 |    8 459   7 |
|    7  89   3 |   48   1   5 |    6   2  49 |
|   24  56  28 |    9 268   7 |    3  45   1 |
+--------------+--------------+--------------+

There's a dozen ways to solve the puzzle from this point, I reckon, but this looks like fun:
(thumbnail)

Not a uniqueness situation, but what with strong links on the 4, 5 and 9, something has to give. Very common situation.

Rather than looking for a loop or chain, a simpler tactic seems to be testing values other than 4, 5 or 9 in the rectangle, especially in the "elbow" cell if there is one. In this puzzle, if a 2 is in r9c1, then both 5 and 9 must be in r7c8.

[wintder]

Skyscraper, Turbot, sashimi x-wing, all names the same for this pattern.

Rare, I would say for a published puzzle.

Code: Select all

+--------------+--------------+--------------+
|    6   3   4 |    1   5   9 |   27  78  28 |
|  *19   2   7 |   38  38   4 |  *19   6   5 |
|    8  19   5 |    6   7   2 |    4  1-9  3 |
+--------------+--------------+--------------+
|   12  18   9 |    7  24   6 |    5   3 248 |
|    3   4  28 |    5   9   1 |   27  78   6 |
|    5   7   6 |   23 234   8 |   19 149 249 |
+--------------+--------------+--------------+
| *249  56   1 |   24  26   3 |    8*459   7 |
|    7  89   3 |   48   1   5 |    6   2  49 |
|   24  56  28 |    9 268   7 |    3  45   1 |
+--------------+--------------+--------------+

You could do y-wing:y-wing styles:w-wing:semi-remote pairs instead?

Edited to correct elimination as per udosuk's comment.

Code: Select all

+--------------+--------------+--------------+
|    6   3   4 |    1   5   9 |   27   78  28 |
|  @19   2   7 |   38  38   4 |   9-1   6   5 |
|    8  9-1  5 |    6   7   2 |    4  @19   3 |
+--------------+--------------+--------------+
|   12  18   9 |    7  24   6 |    5    3 248 |
|    3   4  28 |    5   9   1 |   27   78   6 |
|    5   7   6 |   23 234   8 |   19  149 249 |
+--------------+--------------+--------------+
| *249  56   1 |   24  26   3 |    8 *459   7 |
|    7  89   3 |   48   1   5 |    6    2  49 |
|   24  56  28 |    9 268   7 |    3   45   1 |
+--------------+--------------+--------------+

[udosuk]

Luke, your method is exactly what I posted 11 days ago in this thread. The name of this move is Strong Wing.

Code: Select all

+----------------+----------------+----------------+
| 6    3    4    | 1    5    9    | 27   78   28   |
| 19   2    7    | 38   38   4    | 19   6    5    |
| 8    19   5    | 6    7    2    | 4    19   3    |
+----------------+----------------+----------------+
| 12   18   9    | 7    24   6    | 5    3    248  |
| 3    4    28   | 5    9    1    | 27   78   6    |
| 5    7    6    | 23   234  8    | 19   149  249  |
+----------------+----------------+----------------+
|*249  56   1    | 24   26   3    | 8   *459  7    |
| 7    89   3    | 48   1    5    | 6    2    49   |
|-24   56   28   | 9    268  7    | 3   *45   1    |
+----------------+----------------+----------------+

9 @ r7 locked @ r7c18
4 @ r9 locked @ r9c18
4 @ c1 locked @ r79c1
5 @ c8 locked @ r79c8

r7c8 can't be both 5 & 9 at the same time.
If r7c8<>5, r9c8=5 => r9c1=4
If r7c8<>9, r7c1=9 => r9c1=4

Therefore r9c1 must be 4.


wintder, your Y-wing/W-wing should have eliminated 1 from r2c7+r3c2, not 9 from r2c7.

[daj95376]

Skyscraper, Turbot, sashimi x-wing, all names the same for this pattern.

Rare, I would say for a published puzzle.

Not rare for the Saturday SF Chronicle.

[Luke]

Udosuk: Ah, yes, you are correct. Didn't realize the pattern was exactly the same. I did see that thread, and I should have just posted there with an example of a "strong wing" in the wild.

Wintder, I think you are looking at a different pattern than I. There's many different ways to solve a puzzle this easy, as I mentioned, and yours surely is as good as any!

[submacrolize]

For reference, here is the solution.

[daj95376]

Thank You submacrolize for setting a new standard for obnoxious for the rest of us to strive towards!

[Luke]

For reference, here is the solution.

Wow. I didn't think I'd see Sub's suggestion again after this spanking!

[Luke]

Skyscraper, Turbot, sashimi x-wing, all names the same for this pattern.

Rare, I would say for a published puzzle.

Code: Select all

+--------------+--------------+--------------+
|    6   3   4 |    1   5   9 |   27  78  28 |
|  *19   2   7 |   38  38   4 |  *19   6   5 |
|    8  19   5 |    6   7   2 |    4  1-9  3 |
+--------------+--------------+--------------+
|   12  18   9 |    7  24   6 |    5   3 248 |
|    3   4  28 |    5   9   1 |   27  78   6 |
|    5   7   6 |   23 234   8 |   19 149 249 |
+--------------+--------------+--------------+
| *249  56   1 |   24  26   3 |    8*459   7 |
|    7  89   3 |   48   1   5 |    6   2  49 |
|   24  56  28 |    9 268   7 |    3  45   1 |
+--------------+--------------+--------------+

You could do y-wing:y-wing styles:w-wing:semi-remote pairs instead?

Edited to correct elimination as per udosuk's comment.

Code: Select all

+--------------+--------------+--------------+
|    6   3   4 |    1   5   9 |   27   78  28 |
|  @19   2   7 |   38  38   4 |   9-1   6   5 |
|    8  9-1  5 |    6   7   2 |    4  @19   3 |
+--------------+--------------+--------------+
|   12  18   9 |    7  24   6 |    5    3 248 |
|    3   4  28 |    5   9   1 |   27   78   6 |
|    5   7   6 |   23 234   8 |   19  149 249 |
+--------------+--------------+--------------+
| *249  56   1 |   24  26   3 |    8 *459   7 |
|    7  89   3 |   48   1   5 |    6    2  49 |
|   24  56  28 |    9 268   7 |    3   45   1 |
+--------------+--------------+--------------+

Wintder, I'd like to thank you for mentioning the y-wing here. I was unfamiliar with this technique!

Lessee if I've got this straight. The strong link on 9 in row 7 means that no matter where the 9 goes in row 7, either r2c1 or r3c8 will have to be 1. So whatever cell containing 1 that can see both these cells cannot contain 1!

So the idea is, when the puzzle contains several identical bivalue cells not in the same house, it's a good idea to see if a strong link exists that will bridge either of the two values in said bivalue cells. The value not involved with the strong "bridge' link becomes the potential victim .

This is why I hang around in this forum. I've been missing out! Thanks.

[daj95376]

You could do y-wing:y-wing styles:w-wing:semi-remote pairs instead?

Y-Wing does not belong in this list. A Y-Wing is the same thing as an XY-Wing.

It goes back to Steve K saying Y-Wing Styles was similar to Y-Wing. Now, it seems everyone wants to call it a Y-Wing (for short).

To my knowledge, Y-Wing Styles and W-Wing are limited to four cells. However, I know of at least one example where the Semi-Remote Naked Pair is used with more than four cells.

[ronk]

Yes, it's long past time to deep-six the "y-wing" and "semi-remote pair" names.

"Y-wing" has baggage attached, specifically the xy-chain interpretation from "y-cycle" and "bidirectional y-cycle."

"Semi-remote pair" is simply too long.

[Luke]

Yes, it's long past time to deep-six the "y-wing" and "semi-remote pair" names.

"Y-wing" has baggage attached, specifically the xy-chain interpretation from "y-cycle" and "bidirectional y-cycle."

"Semi-remote pair" is simply too long.

Ok, now don't go getting me confused so soon after my little epiphany .

Up until this thread, this was the extent of my "y-wing" acumen:

Thumbnail (Thank you Scanraid.com)



The pattern Wintder pointed out bears little resemblance to this, save for the underlying concept. I guess it doesn't matter what a technique is called as long as one can utilize it, but I would like to use the proper nomenclature.

So then. What is the proper name for the technique pointed out by Wintder?

[hobiwan]

Up until this thread, this was the extent of my "y-wing" acumen:

Thumbnail (Thank you Scanraid.com)

I think most people around here would call that XY-Wing.

So then. What is the proper name for the technique pointed out by Wintder?

In this forum it's mostly called W-Wing.

[Luke]

Up until this thread, this was the extent of my "y-wing" acumen:

Thumbnail (Thank you Scanraid.com)

I think most people around here would call that XY-Wing.

So then. What is the proper name for the technique pointed out by Wintder?

In this forum it's mostly called W-Wing.

Got it. Thanks.

Here's where I got the idea this was a y-wing.

[keith]

I attempted to summarize an explanation here:

http://www.dailysudoku.co.uk/sudoku/forums/viewtopic.php?t=2143

Keith