stuck on book 1, #70

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stuck on book 1, #70

Postby blairallen » Tue Feb 28, 2006 7:22 am

I'm looking for a suggestion on the next move to solve this puzzle. Here is where I am:

Code: Select all
2 8 . ! . . 5 ! . . 4
9 3 . ! 2 . 7 ! 8 5 .
. . . ! . 8 . ! 2 . .
------------------------
. . 9 ! . . 2 ! 4 3 .
3 . 2 ! . . . ! 5 . .
8 4 5 ! 6 . . ! . . 2
------------------------
. 9 8 ! . 2 . ! . 4 .
4 2 6 ! 1 . 9 ! . 8 5
7 . 3 ! 4 . 8 ! . 2 9


Thanks, Blair
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Postby tarek » Tue Feb 28, 2006 9:53 am

hi there,

There is no way of guessing where you've reached in your solution, if you post your pencilmarks, a clearer view of what you did can be assessed.

This is probably where you've reacched.......

Code: Select all
*-----------------------------------------------------------------*
| 2      8      17    | 39     1369   5     | 13679  1679   4     |
| 9      3      14    | 2      146    7     | 8      5      16    |
| 156    1567   147   | 39     8      1346  | 2      1679   1367  |
|---------------------+---------------------+---------------------|
| 16     167    9     | 578    157    2     | 4      3      1678  |
| 3      167    2     | 789    1479   14    | 5      1679   1678  |
| 8      4      5     | 6      1379   13    | 179    179    2     |
|---------------------+---------------------+---------------------|
| 15     9      8     | 357    2      36    | 1367   4      1367  |
| 4      2      6     | 1      37     9     | 37     8      5     |
| 7      15     3     | 4      56     8     | 16     2      9     |
*-----------------------------------------------------------------*


The next step would be using a technique called box-line interaction (also called locked candidates)..... in this case look at Column 3 then look closely at box 1

It is funny but if you are also interested the same can be achieved if you look for a naked triple in box 1
Tarek
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An unproper way of sovling difficult 'halfway-solved' Sudoku

Postby kevinzhong2001 » Tue Feb 28, 2006 10:35 pm

:idea:As you can see, the bottow left 9 squares only left 2 remain. Try to guess that one is 1 and the other is 5, then try to solve it. If during the rest of the solving there're two numbers in the same row, column or 3*3 box, then switch the number you are guess around. That might work. I use it all the time when I can't find any number just by looking.(Make sure you mark all the numbers with a sign when you are guess!)
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Postby blairallen » Tue Feb 28, 2006 10:47 pm

Tarek,

Thank you for your reply & help; I'm still confused though. I've spent some time getting up to speed on the various terminology (naked pairs & triples, locked candidates) and still can't see a move based on your suggestions. Here's what I can see (and knew already, though I didn't post my pencilmarks, will do in the future):

-in box 1, column 3, #s 1,4,7 are locked candidates since the rest of column 3 is complete, and these 3 cells form a naked triple
-in box 1, row 3, #s 5,6 are locked candidates in r3c1 & r3c2 due to the other locked candidates, and these two cells form a naked pair
-I still don't know what to do with this information, since there aren't sufficient clues in the rest of the band (that I can see)
-do I now have to move to colouring, x-wing, swordfish etc. techniques to make my next move? I have yet to try these techniques, though I've solved all the other 'difficult' level puzzles in this book without them, and a couple of 'fiendish' ones as well. I also have yet to use guessing / trial-and-error and prefer to avoid it...

let me know what you think!

thanks, Blair
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Find a six!~

Postby kevinzhong2001 » Tue Feb 28, 2006 11:04 pm

a 2 8 . ! . . 5 ! . . 4
b 9 3 . ! 2 . 7 ! 8 5 .
c . . . ! . 8 . ! 2 . .
------------------------
d . . 9 ! . . 2 ! 4 3 .
e 3 . 2 ! . . . ! 5 . .
f 8 4 5 ! 6 . . ! . . 2
------------------------
g . 9 8 ! . 2 .! . 4 .
h 4 2 6! 1 . 9! . 8 5
i 7 . 3 ! 4 . 8! . 2 9
A B C D E F G H I

There's no 6 in Ca,Cb,Cc. So there must be a 6 in Ac or Bc. So there's no6 in rest of row c.(No 6 in Dc and Fc)There's no 6 in Dc and Da. So there must be a 6 in Ea or Eb. Therefore there's no 6 in the rest of E column. Therefore: no 6 in Eh and Ei. There's also no 6 in Dg.THEREFORE:Fg is 6!! After the bottom middle is filled.:idea:
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Postby sweetbix » Wed Mar 01, 2006 12:22 am

Code: Select all
*-----------------------------------------------------------------*
| 2      8      17    | 39     1369   5     | 13679  1679   4     |
| 9      3      14    | 2      146    7     | 8      5      16    |
| 156    1567   147   | 39     8      1346  | 2      1679   1367  |
|---------------------+---------------------+---------------------|
| 16     167    9     | 578    157    2     | 4      3      1678  |
| 3      167    2     | 789    1479   14    | 5      1679   1678  |
| 8      4      5     | 6      1379   13    | 179    179    2     |
|---------------------+---------------------+---------------------|
| 15     9      8     | 357    2      36    | 1367   4      1367  |
| 4      2      6     | 1      37     9     | 37     8      5     |
| 7      15     3     | 4      56     8     | 16     2      9     |
*-----------------------------------------------------------------*


Locked candidates means that that number can go in only one row or column in a box eg the 7s in box 2 can only go in row 2. This means you can remove the 7s everywhere else from row 2 ie r3c2.

The 17 14 147 in box 1 is a naked triple and you can eliminate all other 147s in box 1.

That leaves you with a naked double 56 and you can eliminate all other 56s from row 3.

In row 4 you have another naked double ...:D
Last edited by sweetbix on Tue Feb 28, 2006 8:24 pm, edited 1 time in total.
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...

Postby kevinzhong2001 » Wed Mar 01, 2006 12:24 am

Very confusing.:(
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Postby sweetbix » Wed Mar 01, 2006 12:42 am

It might be less confusing if you used the same method of describing the grid that everyone else does here. The horizontal group of cells is a row and the vertical group is a column. Your Aa is called r1c1 and so on, so that the middle cell is r5c5 and your Ii is r9c9.

Here's what you are saying in this forum's language

the 6 is locked into row 3 in box 1 => remove it from all other cells in row 3

that leaves the 6 locked into column 5 in box 2 => remove it from all other cells in column 5 => r9c5=5

=> r7c6=6
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Postby kevinzhong2001 » Wed Mar 01, 2006 12:49 am

It did get easier and shorter the way you write it.

Thanks for the lesson.
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Postby blairallen » Wed Mar 01, 2006 8:55 am

thanks a million for the collective effort guys - that tip was enough to complete the rest of the puzzle. tough one for a difficult! C Ya in the Fiendish section....

Blair
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re: book 1, #70

Postby Pat » Sun May 14, 2006 9:57 am

blairallen wrote:Here is where I am:
Code: Select all
 2 8 . | . . 5 | . . 4
 9 3 . | 2 . 7 | 8 5 .
 . . . | . 8 . | 2 . .
-------+-------+------
 . . 9 | . . 2 | 4 3 .
 3 . 2 | . . . | 5 . .
 8 4 5 | 6 . . | . . 2
-------+-------+------
 . 9 8 | . 2 . | . 4 .
 4 2 6 | 1 . 9 | . 8 5
 7 . 3 | 4 . 8 | . 2 9


hi blairallen

as pointed out by tarek,
there's a box-line interaction.


specifically:
the 6 for box1
must be in r3;

so, the 6 for c6
has only one place left (not in r3).


just one box-line interaction.
( if you like to use a duo or trio, enjoy it - but it isn't needed for this puzzle. )


which book is this from?
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