How to solve the last few fields?

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How to solve the last few fields?

Postby LilaQ » Mon Apr 27, 2015 8:49 pm

Hi guys,

I've been out of Sudokus for a while, tried to remember / re-learn the most common techniques, but got stuck at this one. (please see attachment)

I know I could just "try & error" with this little amount of field left, but I want to solve this by technique & brain. So if someone could take a look at it (you don't even have to solve it, just maybe give me a hint which strategy would help me with this one), I would be really grateful.

Thanks in advance guys!

Best regards,
LilaQ
Attachments
Bildschirmfoto 2015-04-27 um 22.49.10.png
Bildschirmfoto 2015-04-27 um 22.49.10.png (73.18 KiB) Viewed 363 times
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Re: How to solve the last few fields?

Postby JasonLion » Tue Apr 28, 2015 3:07 am

You have already made some mistakes. There are two 8s in column 6 and two 9s in column 4.

Code: Select all
1 4 . | . . 7 | 9 . .
. . 7 | . . 1 | . 3 .
. . . | 2 . 3 | . . .
------+-------+------
8 . . | 3 . . | . 6 5
3 . . | . . . | 4 . .
4 . 6 | . 2 5 | 1 . .
------+-------+------
7 2 . | 4 . . | 3 . .
6 . . | . 1 2 | . . .
. . . | 7 . 6 | . . 1
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Re: How to solve the last few fields?

Postby LilaQ » Tue Apr 28, 2015 9:47 am

Okay that is embarassing...

I will reset the puzzle and try again, sorry :/
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Re: How to solve the last few fields?

Postby LilaQ » Tue Apr 28, 2015 11:37 am

Okay, I tried again (hopefully without errors this time), but I'm stuck again. How to I approach a situation like this?

It seems like there is no simple way to ID the position of the 4s, 6s and 7s, all have 4 notations left. The 8s and 9s are shattered all over the place.

I tried the basic methods, and also X-Wing, Swordfish, XY-Wing, but to no avail. Maybe I'm just blind, I'd be really grateful for your help.

Would love to hear some hints and improve my sudoku game.

Thanks in advance & best regards
LilaQ
Attachments
Bildschirmfoto 2015-04-28 um 13.32.33.png
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Re: How to solve the last few fields?

Postby Leren » Tue Apr 28, 2015 11:56 am

There is a pointing pair of 5's (* cells) in Box 1 which removes the 5's from r3c57.

Code: Select all
*--------------------------------------------------------------*
| 1     4     3      | 6     58    7      | 9     58    2      |
| 2     689   7      | 589   4589  1      | 568   3     48     |
|*59    689  *58     | 2     489-5 3      | 678-5 1     478    |
|--------------------+--------------------+--------------------|
| 8     1     9      | 3     7     4      | 2     6     5      |
| 3     5     2      | 1     6     89     | 4     7     89     |
| 4     7     6      | 89    2     5      | 1     89    3      |
|--------------------+--------------------+--------------------|
| 7     2     1      | 4     589   89     | 3     589   6      |
| 6     3     58     | 589   1     2      | 578   4     789    |
| 59    89    4      | 7     3     6      | 58    2     1      |
*--------------------------------------------------------------*

Then there is an XWing of 5's (* cells) r17 c58 which removes the 5 from r2c5

Code: Select all
*--------------------------------------------------------------*
| 1     4     3      | 6    *58    7      | 9    *58    2      |
| 2     689   7      | 589   489-5 1      | 568   3     48     |
| 59    689   58     | 2     489   3      | 678   1     478    |
|--------------------+--------------------+--------------------|
| 8     1     9      | 3     7     4      | 2     6     5      |
| 3     5     2      | 1     6     89     | 4     7     89     |
| 4     7     6      | 89    2     5      | 1     89    3      |
|--------------------+--------------------+--------------------|
| 7     2     1      | 4    *589   89     | 3    *589   6      |
| 6     3     58     | 589   1     2      | 578   4     789    |
| 59    89    4      | 7     3     6      | 58    2     1      |
*--------------------------------------------------------------*

Next there is a Skyscraper in 8's (* cells) which removes the 8 from r2c4.

Code: Select all
*--------------------------------------------------------------*
| 1     4     3      | 6    *58    7      | 9    *58    2      |
| 2     689   7      | 59-8  489   1      | 568   3     48     |
| 59    689   58     | 2     489   3      | 678   1     478    |
|--------------------+--------------------+--------------------|
| 8     1     9      | 3     7     4      | 2     6     5      |
| 3     5     2      | 1     6     89     | 4     7     89     |
| 4     7     6      |*89    2     5      | 1    *89    3      |
|--------------------+--------------------+--------------------|
| 7     2     1      | 4     589   89     | 3     589   6      |
| 6     3     58     | 589   1     2      | 578   4     789    |
| 59    89    4      | 7     3     6      | 58    2     1      |
*--------------------------------------------------------------*

A pointing triple of 8's in Box 2 (* cells) removes the 8 from r7c5.

Code: Select all
*--------------------------------------------------------------*
| 1     4     3      | 6    *58    7      | 9     58    2      |
| 2     689   7      | 59   *489   1      | 568   3     48     |
| 59    689   58     | 2    *489   3      | 678   1     478    |
|--------------------+--------------------+--------------------|
| 8     1     9      | 3     7     4      | 2     6     5      |
| 3     5     2      | 1     6     89     | 4     7     89     |
| 4     7     6      | 89    2     5      | 1     89    3      |
|--------------------+--------------------+--------------------|
| 7     2     1      | 4     59-8  89     | 3     589   6      |
| 6     3     58     | 589   1     2      | 578   4     789    |
| 59    89    4      | 7     3     6      | 58    2     1      |
*--------------------------------------------------------------*

Lastly a Skyscraper in 8's (* cells) removes the 8's from r6c8 and r8c9.

Code: Select all
*--------------------------------------------------------------*
| 1     4     3      | 6     58    7      | 9     58    2      |
| 2     689   7      | 59    489   1      | 568   3     48     |
| 59    689   58     | 2     489   3      | 678   1     478    |
|--------------------+--------------------+--------------------|
| 8     1     9      | 3     7     4      | 2     6     5      |
| 3     5     2      | 1     6    *89     | 4     7    *89     |
| 4     7     6      | 89    2     5      | 1     9-8   3      |
|--------------------+--------------------+--------------------|
| 7     2     1      | 4     59   *89     | 3    *589   6      |
| 6     3     58     | 589   1     2      | 578   4     79-8   |
| 59    89    4      | 7     3     6      | 58    2     1      |
*--------------------------------------------------------------*

The puzzle solves with singles after that.

Leren
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Re: How to solve the last few fields?

Postby LilaQ » Tue Apr 28, 2015 2:24 pm

Awesome, I got it. Thanks for the explanation, I wasn't aware of the Skyscraper method, it's really useful. I think it's just hard to see them.

Thanks again!
LilaQ
 
Posts: 6
Joined: 27 April 2015

Re: How to solve the last few fields?

Postby Leren » Tue Apr 28, 2015 8:44 pm

Here's a link to a site that discusses Skyscrapers and a lot of other solving methods. As I say often it's one of the best teaching sites around.

http://hodoku.sourceforge.net/en/techniques.php

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