Need help with difficult (for me) puzzle

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Need help with difficult (for me) puzzle

Postby jvs » Wed Feb 08, 2006 7:29 pm

Here is a puzzle from p 137 of "Grand Master Su Doku" by Wayne Gould.
This puzzle is rated as "Superior", which is the fifth of his five ratings.

I've filled in quite a few entries but am totally stuck. Could someone
show me how to take the next step? Below is the current state of
my solution. I've checked my intermediate results against the answer.

6|2347|37| |349|8|5| |24|1|2479|
24|8|5| |469|7|1| |3|29|2469|
347|9|1| |346|2|346| |68|78|5|
-----------------------------------------
5|16|8| |7|3|2| |9|4|16|
139|135|369| |5|4|8| |16|27|27|
27|27|4| |1|6|9| |58|58|3|
-----------------------------------------
8|134|39| |234|5|34| |7|6|1249|
1347|13467|2| |8|9|3467| |15|35|14|
3479|5|3679| |2346|1|3457| |24|239|8|

The following grid is the original puzzle.

6--|-8-|-1-|
---|-7-|3--|
-91|---|--5|
-------------
5--|--2|9--|
---|5-8|---|
--4|1--|--3|
-------------
8--|---|76-|
--2|-9-|---|
-5-|-1-|--8|
-------------
jvs
 
Posts: 6
Joined: 08 February 2006

Postby vidarino » Wed Feb 08, 2006 7:41 pm

Code: Select all
      6   2347     37  |    349      8      5  |     24      1   2479
     24      8      5  |    469      7      1  |      3     29   2469
    347      9      1  |    346      2    346  |     68     78      5
-----------------------+-----------------------+-----------------------
      5     16*     8  |      7      3      2  |      9      4     16*
    139     13-   369  |      5      4      8  |     16     27     27
     27     27      4  |      1      6      9  |     58     58      3
-----------------------+-----------------------+-----------------------
      8    134*    39  |    234      5     34  |      7      6   1249*
   1347  13467-     2  |      8      9   3467  |     15     35     14-
   3479      5   3679  |   2346      1    347  |     24    239      8


You have an X-Wing with 1s (= two aligned conjugate pairs) in rows 4 and 8. This means you can eliminate 1s from the rest of the columns 2 and 9.

Vidar
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Postby jvs » Wed Feb 08, 2006 8:07 pm

THANK YOU!!!
jvs
 
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Postby tarek » Wed Feb 08, 2006 9:33 pm

Hi jvs,

There are some incorrect eliminations in your pencil marks.



you eliminated 6 from r5c2, How??? The 5 in the same square also should be eliminated as there is a NAKED 5 in the same row.

you eliminated 6 from r9c6, How ??? why (As it is incorrect)???? & again a 5 in the same cell not eliminated as there is a Naked 5 in the same row.

Is it a case of 6 being next to 5 on the keyboard:D

Tarek
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Postby Tumbleweed » Thu Feb 09, 2006 1:18 am

vidarino wrote:
Code: Select all
      6   2347     37  |    349      8      5  |     24      1   2479
     24      8      5  |    469      7      1  |      3     29   2469
    347      9      1  |    346      2    346  |     68     78      5
-----------------------+-----------------------+-----------------------
      5     16*     8  |      7      3      2  |      9      4     16*
    139     13-   369  |      5      4      8  |     16     27     27
     27     27      4  |      1      6      9  |     58     58      3
-----------------------+-----------------------+-----------------------
      8    134*    39  |    234      5     34  |      7      6   1249*
   1347  13467-     2  |      8      9   3467  |     15     35     14-
   3479      5   3679  |   2346      1    347  |     24    239      8


You have an X-Wing with 1s (= two aligned conjugate pairs) in rows 4 and 8. This means you can eliminate 1s from the rest of the columns 2 and 9.

Vidar


Did you mean rows 4 & 7? (where the * are?). I'm still struggling to understand xwing. I see why the 16's are paired, but why have you paired the 134 with the 1249 on row 7, rather than the rows below, the 13467 with the 14?

Many thanks
Tumbleweed
 
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Joined: 22 July 2005

Postby vidarino » Thu Feb 09, 2006 1:32 am

X-Wing works like this:

There are two rows (4 and 7 in this case) which only have two cells for a certain candidate (1), and the two spots happen to fall on the same columns. This leaves us with only two possible combinations for placement of the 1s in these rows:
Code: Select all
R4 -1- --- --.
R7 -.- --- --1

or
Code: Select all
R4 -.- --- --1
R7 -1- --- --.


Now, we can't say which one is the right one, but we *can* see that no matter which it is, there will be a 1 in column 2 and one in column 9. Therefore we can eliminate 1s from the rest of the columns.

(Edit: Correct row numbers.)
Last edited by vidarino on Thu Feb 09, 2006 5:03 am, edited 1 time in total.
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Need help with difficult (for me) puzzle

Postby Cec » Thu Feb 09, 2006 5:28 am

vidarino wrote:This leaves us with only two possible combinations for placement of the 1s in these rows:
Code: Select all
R4 -1- --- --.
R9 -.- --- --1

or
Code: Select all
R4 -.- --- --1
R9 -1- --- --.



Shouldn't this be row 7 not row 9?

Cec
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Re: Need help with difficult (for me) puzzle

Postby vidarino » Thu Feb 09, 2006 9:04 am

cecbevwr wrote:Shouldn't this be row 7 not row 9?


Oops, indeed. That's the second time in this thread I mess up.

Anyway, edited. Thanks.
vidarino
 
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Joined: 02 January 2006

Postby Tumbleweed » Thu Feb 09, 2006 9:50 am

vidarino wrote:X-Wing works like this:

There are two rows (4 and 7 in this case) which only have two cells for a certain candidate (1), and the two spots happen to fall on the same columns. This leaves us with only two possible combinations for placement of the 1s in these rows:
Code: Select all
R4 -1- --- --.
R7 -.- --- --1

or
Code: Select all
R4 -.- --- --1
R7 -1- --- --.


Now, we can't say which one is the right one, but we *can* see that no matter which it is, there will be a 1 in column 2 and one in column 9. Therefore we can eliminate 1s from the rest of the columns.

(Edit: Correct row numbers.)


Got it, thanks, thats by far the clearest explanation I've ever seen!

tw
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Need help with difficult (for me) puzzle

Postby Cec » Thu Feb 09, 2006 10:31 am

Tumbleweed wrote:Got it, thanks, thats by far the clearest explanation I've ever seen!


Yes - I thought it was well presented too.
Cec
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