## OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

Post the puzzle or solving technique that's causing you trouble and someone will help

### OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

Hi, all,

I have always problems in solving Sudoku

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

Because of not finding ANY hidden single - I had to pencilmark ALL 57 remaining cells. This Sudoku has 24 given numbers.

Code: Select all
`+------------------+----------------+-----------------+|7... 345... 9.....|1456 1346. 135..|8.... 135... 2...||1346 2345.. 123456|7... 12346 8....|1356. 1359.. 3569||8... 235... 12356.|1569 1236. 12359|13567 1359.. 4...|+------------------+----------------+-----------------+|349. 6..... 234...|148. 5.... 12...|1234. 7..... 389.||49.. 245789 2457..|3... 12478 6....|1245. 124589 589.||34.. 1..... 23457.|48.. 9.... 27...|2345. 6..... 358.|+------------------+----------------+-----------------+|2... 3479.. 3467..|5689 3678. 3579.|3456. 3458.. 1...||1369 379... 1367..|2... 13678 4....|356.. 358... 3568||5... 34.... 8.....|16.. 136.. 13...|9.... 234... 7...|+------------------+----------------+-----------------+`

I needed more than one hour for the pencilmarking - but no solution...

Any tipps are appreciated.

Greetings
NoClue
NoClue

Posts: 48
Joined: 01 April 2011

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

Code: Select all
`_        Hidden Single                   =  2    r9c8_        Hidden Single                   =  7    r3c7_        Hidden Single                   =  8    r5c2_        Hidden Single                   =  4    r9c2`
daj95376
2014 Supporter

Posts: 2624
Joined: 15 May 2006

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

Hi NoClue,

Hidden Singles IMO are easiest to find ....

Start by looking at the 8 in column 1 then the 8 in column 3 ...
Then look at box 1 & box 7
Column 2 doesn't have an 8 yet, box 2 doesn't have an 8 yet ...

Where do you think that 8 should be ???

tarek

Posts: 2650
Joined: 05 January 2006

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

Hi, tarek,

I only found 4 hidden singles:

1. r3c7 = 7
2. r5c2 = 8
3. r9c2 = 4
4. r9c8 = 2

then I get stuck ... .-(

Greetings
NoClue
NoClue

Posts: 48
Joined: 01 April 2011

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

This puzzle goes beyond singles ...

The technique that your after is what I call box-line reduction.

There are many names that this technique has had. Look at intersections, Pointing and Claiming.

You need to train your eyes to look for them.

tarek

tarek

Posts: 2650
Joined: 05 January 2006

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

Hi, tarek,

is that a box-line reduction?

- candidate "1" in box 8 is in line 9
- can I eliminate "1" at r8c5?

Greetings
Lothar
NoClue

Posts: 48
Joined: 01 April 2011

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

NoClue, I have repeatedly asked you to put your puzzles in one thread. To keep things reasonably organized in that one thread, I recommend you arrive at a conclusion for one puzzle before posting the next puzzle.

In keeping with the above, I have deleted the puzzle you posted about 30 minutes after this one.
ronk-Moderator
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Joined: 02 November 2005
Location: Southeastern USA

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

NoClue wrote:Hi, tarek,

is that a box-line reduction?

- candidate "1" in box 8 is in line 9
- can I eliminate "1" at r8c5?

NoClue,

There are some basic fundamentals that you need to grasp fully before you move to the next level. I was quite surprised about your previous question about hidden singles! I suggest that you dshouldn't go beyond that level before you master it completely. I was at that stage once upon a time.

here is the suggested move I was talking about
Code: Select all
`*--------------------------------------------------------------------------*| 7       35      9      | 1456    1346    135    | 8       135     2      || 1346    235     123456 | 7       12346   8      | 1356    1359    3569   || 8       235     12356  | 1569    1236    12359  | 7       1359    4      ||------------------------+------------------------+------------------------|| 349     6       234    | 148     5       12     | 1234    7       389    || 49      8       2457   | 3       1247    6      | 1245    1459    59     || 34      1       23457  | 48      9       27     | 2345    6       358    ||------------------------+------------------------+------------------------|| 2       379     367    | 5689    3678    3579   | 3456    3458    1      || 1369    379     1367   | 2       13678   4      | 356     358     3568   || 5       4       8      | 16      136     13     | 9       2       7      |*--------------------------------------------------------------------------*`
Look at column 2. The only possibilities in that column to have 2s is in r2c2 & r3c2. These 2 cells are also in box 1. That means that any other possibility in that box that has 2 in box 1 can be eliminated (r2c3 & r3c3).

tarek

Posts: 2650
Joined: 05 January 2006

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

Hi, tarek,

thanks for the explanation - but - I have to confess that I have the biggest problems with Line-Box-Reduction and Box-Line-Reduction. That was the reason I asked you if I was right with assuming box 8 and line 9 (candidate "1") and eliminating "1" at r8c5.

Greetings
NoClue
NoClue

Posts: 48
Joined: 01 April 2011

### Re: OsnabrÃ¼cker Sonntagszeitung 22.05.2011 - Sudoku schwer

NoClue wrote: That was the reason I asked you if I was right with assuming box 8 and line 9 (candidate "1") and eliminating "1" at r8c5.

That is a correct elimination ... It is indeed a Line-Box reduction

All the 1s in line 9 are confined to one box, any 1s in that box but outside that line can be eliminated. That is r8c5<>1

tarek

tarek

Posts: 2650
Joined: 05 January 2006