stuck on a puzzle - NY Post fiendish

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stuck on a puzzle - NY Post fiendish

Postby confuzed » Tue Nov 18, 2008 6:04 am

I have gotten this far on one of the puzzles in this book:

Code: Select all
 *-----------------*
 |. . .|4 6 .|. 2 .|
 |. . .|7 . 8|. . .|
 |. 6 4|2 3 1|9 5 .|
 |-----+-----+-----|
 |. 8 2|. . .|5 7 .|
 |. 5 .|8 . .|2 1 .|
 |. 9 3|. . .|4 8 .|
 |-----+-----+-----|
 |5 4 1|9 8 6|7 3 2|
 |. . .|5 . 2|. . .|
 |. 2 .|. 7 .|. . .|
 *-----------------*


I've been forced to use t/e a lot in this book so far (this is only the 15th puzzle) and I find that while t/e almost always leads me to the solution, it removes a lot of fun from finding the solution. But if I don't use t/e what else can I use, it looks to me like I've exhausted every other method but maybe there is something obvious that I overlooked?
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Postby hobiwan » Tue Nov 18, 2008 7:12 am

Look at row 2: there is only one possibility for digit 2.
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Postby confuzed » Tue Nov 18, 2008 3:08 pm

Wow, thanks, I can't believe I overlooked that. Yes, this helps tremendously, thank you.
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Postby confuzed » Wed Nov 19, 2008 5:06 am

Here is a much harder one from p.19, again already solved to the point of needing t/e
Code: Select all
 *-----------------*
 |. 2 .|. . 4|. 8 6|
 |. 8 4|. 2 .|9 . 7|
 |9 1 .|. . .|. 2 4|
 |-----+-----+-----|
 |. . 8|3 . .|. . .|
 |. . 9|. 1 .|7 . 8|
 |. . .|. . 8|2 . .|
 |-----+-----+-----|
 |. . .|. . .|. 5 1|
 |4 5 2|. 7 .|8 . .|
 |8 . 1|5 . .|. 7 2|
 *-----------------*

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Postby confuzed » Wed Nov 19, 2008 5:40 am

And another one on the next page that cannot be solved without t/e. I thought Gould's puzzles did not require guesswork (at least that's what the book's introduction says). Maybe I'm doing these the wrong way?

Code: Select all
 *-----------------*
 |. . 7|. . 9|3 4 .|
 |. . 6|. 3 4|9 . .|
 |3 4 9|2 8 .|. . 5|
 |-----+-----+-----|
 |. 9 .|4 . 1|2 5 .|
 |. 1 .|. . .|. 9 .|
 |. 6 5|9 . 3|. . .|
 |-----+-----+-----|
 |9 7 .|. 1 2|5 3 .|
 |. 3 .|. 9 .|. . .|
 |. 5 1|3 4 .|8 . 9|
 *-----------------*

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Postby hobiwan » Wed Nov 19, 2008 9:08 am

confuzed wrote:I thought Gould's puzzles did not require guesswork (at least that's what the book's introduction says). Maybe I'm doing these the wrong way?

All the puzzles you have posted so far can be solved using rather easy techniques. If you are relatively new to the game I suggest you take a look at Sudopedia. Check out the techniques described in "Intersections".

A sample solution for your puzzle p.19:
Code: Select all
.-------------------.---------------------.------------------.
| 357    2     357  | 179    359    4     | 135   8      6   |
| 356    8     4    | 16     2      1356  | 9     13     7   |
| 9      1     3567 | 678    3568   3567  | 35    2      4   |
:-------------------+---------------------+------------------:
| 12567  467   8    | 3      4569   25679 | 1456  1469   59  |
| 2356   346   9    | 246    1      256   | 7     346    8   |
| 13567  3467  3567 | 4679   4569   8     | 2     13469  359 |
:-------------------+---------------------+------------------:
| 367    3679  367  | 24689  34689  2369  | 346   5      1   |
| 4      5     2    | 169    7      1369  | 8     369    39  |
| 8      369   1    | 5      3469   369   | 346   7      2   |
'-------------------'---------------------'------------------'
Locked Candidates Type 1 (Pointing): 9 in b9 => r8c46<>9
Naked Pair: 1,6 in r28c4 => r1c4<>1, r3567c4<>6
Singles to end
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Postby confuzed » Wed Nov 19, 2008 10:46 am

It's fair (and fairly obvious I'd assume) that I'm new to this level of sudoku. I understand the theory behind the theory behind these basic solving techniques but applying them has been a struggle for me. I appreciate your help on these.
I had spotted the Locked Candidates and Naked Pair on p.19, but I don't understand how these allow for Singles to end. In this case, those strategies only eliminate a few possibilities without telling me where to place any numbers. In other words, I don't understand how Singles to end follows from this reasoning.
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Postby hobiwan » Thu Nov 20, 2008 9:59 am

confuzed wrote:In other words, I don't understand how Singles to end follows from this reasoning.


This is the state of the puzzle after the Naked Pair:
Code: Select all
.-------------------.--------------------.-----------------.
| 357    2     357  | 79    359    4     | 135  8      6   |
| 356    8     4    | 16    2      1356  | 9    13     7   |
| 9      1     3567 | 78    3568   3567  | 35   2      4   |
:-------------------+--------------------+-----------------:
| 12567  467   8    | 3     4569   25679 | 16   1469   59  |
| 2356   346   9    | 24    1      256   | 7    346    8   |
| 13567  3467  3567 | 479   4569   8     | 2    13469  359 |
:-------------------+--------------------+-----------------:
| 367    3679  367  | 2489  34689  2369  | 346  5      1   |
| 4      5     2    | 16    7      136   | 8    369    39  |
| 8      369   1    | 5     3469   369   | 346  7      2   |
'-------------------'--------------------'-----------------'

A possible beginning:
Hidden Single: r1c7=1
Hidden Single: r3c7=5
Full House: r2c8=3
Hidden Single: r6c9=3
Hidden Single: r4c9=5
Full House: r8c9=9
Hidden Single: r8c6=3
Hidden Single: r8c4=1
Full House: r8c8=6
Hidden Single: r2c6=1
Hidden Single: r1c5=5
Hidden Single: r2c1=5
Hidden Single: r2c1=5
...

The first hidden Single is the only one present in the grid at that moment so it is easy to overlook.
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Postby confuzed » Sun Nov 23, 2008 5:39 am

Easy to overlook, I don't think I would have seen that hidden single in a million years without your help. But it was very easy to finish after finally seeing that hidden single in r1c7. I finished the next few puzzles as well, and had to guess on p.20 and p.22 but not p.21 and p.23. I guess even at the "fiendish" level some are less difficult than others.
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Postby confuzed » Sun Nov 23, 2008 5:53 am

Also, I downloaded Simple Sudoku and will try using it for hints when I'm stuck. I think it will be a tremendous help to me.
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Postby Pat » Sun Nov 23, 2008 6:14 am

confuzed wrote:Easy to overlook,
I don't think I would have seen that hidden single in a million years without your help.


yes, i can still miss a "single"
and go looking for something tougher---


confuzed wrote:had to guess on p.20 and p.22


use guessing if you like --
but it's never needed for Pappocom puzzles
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Postby Pat » Sun Nov 23, 2008 6:31 am

        is this the puzzle from page 20 ?
Code: Select all
 . . 7 | . . 9 | 3 4 .
 . . 6 | . 3 4 | 9 . .
 3 4 9 | 2 8 . | . . 5
-------+-------+------
 . 9 . | 4 . 1 | 2 5 .
 . 1 . | . . . | . 9 .
 . 6 5 | 9 . 3 | . . .
-------+-------+------
 9 7 . | . 1 2 | 5 3 .
 . 3 . | . 9 . | . . .
 . 5 1 | 3 4 . | 8 . 9



tricky indeed---
    "hidden" duo {1,5} in box 1
    ==> "hidden" duo {2,8} in row 1
    ==> the 6 for box 3 must be in row 3
    ==> "naked single" in r3c6
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