hard puzzle for solving again! number 4.

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hard puzzle for solving again! number 4.

Postby fredooi » Sun Aug 24, 2008 7:47 am

it's the sunday newspaper again....can't solve it!!...so sad....

this time i'll just paste the one with pencilmarks...

Code: Select all
1   49  6    | 74  5   8   | 379  37   2   |
3   8   49   | 74  1   2   | 79   56   56  |
7   5   2    | 3   6   9   | 1    4    8   |
-------------+-------------+---------------|
9   6   5    | 8   3   17  | 4    2    17  |
4   3   1    | 5   2   67  | 8    67   9   |
8   2   7    | 16  9   4   | 5    136  136 |
-------------+-------------+---------------|
6   1   8    | 2    4  5   | 73   9    73  |
2   7   349  | 19   8  13  | 6    15   145 |
5   49  349  | 169  7  136 | 2    8    14  |
--------------------------------------------
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Postby daj95376 » Sun Aug 24, 2008 9:00 am

There's a 4-cell XY-Chain that cracks the puzzle, but I'm surprised that it would appear in a newspaper.

Code: Select all
 XY-Chain (a-d)
 +-----------------------------------------------------+
 |  1    49   6    |  47   5    8    |  379  37   2    |
 |  3    8    49   |  47   1    2    |  79  c56   56   |
 |  7    5    2    |  3    6    9    |  1    4    8    |
 |-----------------+-----------------+-----------------|
 |  9    6    5    |  8    3    17   |  4    2   a17   |
 |  4    3    1    |  5    2    67   |  8   b67   9    |
 |  8    2    7    |  16   9    4    |  5    36-1 136  |
 |-----------------+-----------------+-----------------|
 |  6    1    8    |  2    4    5    |  37   9    37   |
 |  2    7    349  |  19   8    13   |  6   d15   45-1 |
 |  5    49   349  |  169  7    136  |  2    8    4-1  |
 +-----------------------------------------------------+
 # 36 eliminations remain
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Postby tarek » Sun Aug 24, 2008 9:04 am

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

*-----------------------------------------------*
| 1    49   6   | 47   5    8   | 379  37   2   |
| 3    8    49  | 47   1    2   | 79   56   56  |
| 7    5    2   | 3    6    9   | 1    4    8   |
|---------------+---------------+---------------|
| 9    6    5   | 8    3    17  | 4    2    17  |
| 4    3    1   | 5    2    67  | 8    67   9   |
| 8    2    7   |*16   9    4   | 5   *136  136 |
|---------------+---------------+---------------|
| 6    1    8   | 2    4    5   | 37   9    37  |
| 2    7    349 |*19   8   -13  | 6   *15   145 |
| 5    49   349 |#169  7    136 | 2    8    14  |
*-----------------------------------------------*
*-----------------------------------------------*
| 1    49   6   | 47   5    8   | 379  37   2   |
| 3    8    49  | 47   1    2   | 79   56   56  |
| 7    5    2   | 3    6    9   | 1    4    8   |
|---------------+---------------+---------------|
| 9    6    5   | 8    3   *17  | 4    2   *17  |
| 4    3    1   | 5    2    67  | 8    67   9   |
| 8    2    7   | 16   9    4   | 5    136  136 |
|---------------+---------------+---------------|
| 6    1    8   | 2    4    5   | 37   9    37  |
| 2    7    349 | 19   8   -13  | 6    15   145 |
| 5    49   349 |#169  7   *136 | 2    8   *14  |
*-----------------------------------------------*
Eliminating 1 From r8c6 (Finned XWing in Columns 48 with 1 fins in Box 8, or by constructing the Finned XWing in rows 49 with 1 fin in Box 8) Ultimately not needed
.
.
.
Singles
.
.
.
*-----------------------------------------------*
| 1    49   6   | 47   5    8   | 379  37   2   |
| 3    8    49  | 47   1    2   | 79  *56   56  |
| 7    5    2   | 3    6    9   | 1    4    8   |
|---------------+---------------+---------------|
| 9    6    5   | 8    3    17  | 4    2   %17  |
| 4    3    1   | 5    2    67  | 8   %67   9   |
| 8    2    7   | 16   9    4   | 5   -136  136 |
|---------------+---------------+---------------|
| 6    1    8   | 2    4    5   | 37   9    37  |
| 2    7    49  | 19   8    3   | 6   *15  -145 |
| 5    49   3   | 169  7    16  | 2    8   -14  |
*-----------------------------------------------*
Eliminating 1 from r6c8,r89c9(ALS-XZ A=156 in r28c8 B=167 in r5c8, r4c9  x=6 z=1)
.
.
.
Singles
.
.
.
Solution
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Postby katherine_china » Sun Aug 24, 2008 9:16 am

hello fredooi
my next step is r6c4-->r8c4
if r6c4=6,than r4c6=7-->r5c6=7-->r5c8=6-->r8c8=1-->r8c4=9
if r6c4=1,than r8c4=9
so either r6c4=6or1,r8c4=9
we call it"bao li"in chinese.maybe it's like "forcing chain".:D
it's very useful in hard sudoku puzzles.
we often say that"bao li wan sui",maybe you will like it.

than you can use finnd fish or single chain(Skyscraper) to solve it.
finned fish:(X-wing R4C69,R9C69 fin R9C4) than 1 is eliminated in r8c6
single chain:r9c4(1)==r6c4(1)--r6c8(1)==r8c8(1) than 1 is eliminated in r8c6
choose one you like:D
Last edited by katherine_china on Sun Aug 24, 2008 6:08 am, edited 1 time in total.
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Postby Pat » Sun Aug 24, 2008 9:35 am

katherine_china wrote:my next step is r6c4-->r8c4
    if r6c4=6,than r4c6=7-->r4c9=1-->r9c9=4-->r9c4=1-->r8c4=9
    if r6c4=1,than r8c4=9
so either r6c4=6or1,r8c4=9


no
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Postby katherine_china » Sun Aug 24, 2008 10:10 am

Pat wrote:
katherine_china wrote:my next step is r6c4-->r8c4
    if r6c4=6,than r4c6=7-->r4c9=1-->r9c9=4-->r9c4=1-->r8c4=9
    if r6c4=1,than r8c4=9
so either r6c4=6or1,r8c4=9


no

sorry for a mistake.:(
it's correct now
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Postby fredooi » Sun Aug 24, 2008 9:20 pm

wow, so many ways to solve this...thanks to all!

i was thinking to solve this with forcing chain too, but i guess i haven't learn it well enough to notice them in this puzzle.

to katherine, i am a chinese. a malaysian chinese....therefore i understand what you says~~~
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Posts: 14
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Re: hard puzzle for solving again! number 4.

Postby udosuk » Mon Aug 25, 2008 1:20 pm

Code: Select all
+--------------+-------------+---------------+
| 1   49  6    | 74  5   8   | 379  37   2   |
| 3   8   49   | 74  1   2   | 79  *56   56  |
| 7   5   2    | 3   6   9   | 1    4    8   |
+--------------+-------------+---------------+
| 9   6   5    | 8   3   17  | 4    2   #17  |
| 4   3   1    | 5   2   67  | 8   *67   9   |
| 8   2   7    | 16  9   4   | 5   -136  136 |
+--------------+-------------+---------------+
| 6   1   8    | 2    4  5   | 73   9    73  |
| 2   7   349  | 19   8  13  | 6   #15  -145 |
| 5   49  349  | 169  7  136 | 2    8   -14  |
+--------------+-------------+---------------+

The most critical move have been showed as an xy-chain or ALS-xz above, but it can also be quite elegantly expressed as the following:

Grouped xy-wing:
r25c8, as a group, must have 5 or 7 or both
=> one or both of r4c9+r8c8 must be 1
=> r6c8+r89c9, seeing r4c9+r8c8, can't be 1

All naked singles from here.

(Note that only the elimination from r9c9 is required here.)

katherine_china wrote:we call it"bao li"in chinese.maybe it's like "forcing chain".:D
it's very useful in hard sudoku puzzles.
we often say that"bao li wan sui",maybe you will like it.

fredooi wrote:to katherine, i am a chinese. a malaysian chinese....therefore i understand what you says~~~

To all those who don't speak Chinese, "bao li" means "violence" or "brute force". Thus "bao li wan sui" means "long live violence" or "long live brute force".:idea:

For this puzzle you obviously don't need any violence or brute force if you're smart enough.:)

I've been in Malaysia for an extended period of time recently and I never bothered to try any puzzle from the Star newspaper. Apparently they have a high expectation of their readers' IQ. Wonder what's the difficulty level of puzzles from Chinese papers.:?:
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