The New Sudoku Players' Forum

[jvs]

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|
-------------

[vidarino]

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

[jvs]

THANK YOU!!!

[tarek]

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

Tarek

[Tumbleweed]

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

[vidarino]

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.)

[Cec]

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

[vidarino]

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.

[Tumbleweed]

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

[Cec]

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

Yes - I thought it was well presented too.
Cec