stuck, need help

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stuck, need help

Postby Drjay » Sat Aug 08, 2015 4:43 pm

Hello friends !

I'm interested in how to solve this Sudoku :

Image

Thanks in advance!
Drjay
 
Posts: 10
Joined: 30 July 2015

Re: stuck, need help

Postby JC Van Hay » Sat Aug 08, 2015 6:44 pm

Hints :
1. Pay attention, now or later : beyond locked candidates, only a candidate for the digit 1|6|8 can be excluded by the solutions of the digit 1|6|8 respectively.
2. It would be interesting to analyze the puzzle from the 2 solutions of C3 + B7!
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Re: stuck, need help

Postby Drjay » Sat Aug 08, 2015 7:26 pm

First of all, thanks for the fast reply.

JC Van Hay wrote:Hints :
1. Pay attention, now or later : beyond locked candidates, only a candidate for the digit 1|6|8 can be excluded by the solutions of the digit 1|6|8 respectively.

Sorry but my english is not the best, what exactly do you mean by saying that?

2. It would be interesting to analyze the puzzle from the 2 solutions of C3 + B7!

What are "C3 + B7"? "Column 3 + ?" ?
Drjay
 
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Re: stuck, need help

Postby daj95376 » Sat Aug 08, 2015 8:02 pm

There is a pattern in <6> that cracks the puzzle at this point.

Code: Select all
 +-----------------------------------------------------------------------+
 |  3      5      1-6    |  9      4      678    | a26     168    12678  |
 |  7      2      4      |  18     568    3      |  9      1568   1568   |
 |  168    18     9      |  127    256    567    |  4      3      1567   |
 |-----------------------+-----------------------+-----------------------|
 |  1268   148    7      |  3      2568   4568   | b256    9      1268   |
 |  5      48    d26     |  248    1      9      |  7     c468    3      |
 |  1268   9      3      |  2478   2568   45678  | b256    1468   1268   |
 |-----------------------+-----------------------+-----------------------|
 |  9      6      8      |  5      3      2      |  1      7      4      |
 |  12     7      12     |  48     9      48     |  3      56     56     |
 |  4      3      5      |  6      7      1      |  8      2      9      |
 +-----------------------------------------------------------------------+
 # 80 eliminations remain

 6r1c7                               -6 r1c3

 6r1c7 = 6r46c7 - 6r5c8 = 6r5c3  =>  -6 r1c3

Translation:

Code: Select all
If <6> is true  in r1c7,  then <6> must be false in r1c3

If <6> is false in r1c7,  then <6> must be true  in one of r46c7 ...
if <6> is true  in r46c7, then <6> must be false in r5c8 ...
if <6> is false in r5c8,  then <6> must be true  in r5c3 ...
if <6> is true  in r5c3,  then <6> must be false in r1c3.

Whether <6> is true/false in r1c7, we get the common outcome that <6> is false in r1c3.

This pattern is called a 2-String Kite. The kite is [box 6], the first string is [column 7], and the second string is [row 5].

BTW: Nice graphic image.

_
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Re: stuck, need help

Postby Drjay » Sun Aug 09, 2015 2:26 pm

Thanks! You helped me a lot.
Drjay
 
Posts: 10
Joined: 30 July 2015

Re: stuck, need help

Postby Drjay » Sun Aug 09, 2015 6:42 pm

Maybe you could help me with this one as well :

Image

I'm not much into more advanced techniques yet.
Drjay
 
Posts: 10
Joined: 30 July 2015

Re: stuck, need help

Postby Leren » Sun Aug 09, 2015 8:31 pm

There is Swordfish of 7's in Rows 247 Columns 246 which removes 7 from r5c6 and r9c4. I've marked the Swordfish cells with * in the diagram.

Code: Select all
*--------------------------------------------------------------*
| 5     4     1      | 3     8     6      | 79    2     79     |
| 6     8     9      |*27    5    *27     | 4     3     1      |
| 7     2     3      | 1     9     4      | 58    6     58     |
|--------------------+--------------------+--------------------|
| 9    *57    2      | 8     3    *57     | 1     4     6      |
| 3     1     57     | 6     4     25-7   | 2789  89    789    |
| 8     6     4      | 9     27    1      | 257   57    3      |
|--------------------+--------------------+--------------------|
| 2    *57    6      |*57    1     3      | 89    89    4      |
| 1     9     57     | 4     6     8      | 3     57    2      |
| 4     3     8      | 25-7  27    9      | 6     1     57     |
*--------------------------------------------------------------*

Next there is a Skyscraper in 7's in the cells I've marked abcd which removes the 7's from r5c79.

Code: Select all
*--------------------------------------------------------------*
| 5     4     1      | 3     8     6      | 79    2     79     |
| 6     8     9      | 27    5     27     | 4     3     1      |
| 7     2     3      | 1     9     4      | 58    6     58     |
|--------------------+--------------------+--------------------|
| 9     57    2      | 8     3     57     | 1     4     6      |
| 3     1    a57     | 6     4     25     | 289-7 89    89-7   |
| 8     6     4      | 9     27    1      | 257  d57    3      |
|--------------------+--------------------+--------------------|
| 2     57    6      | 57    1     3      | 89    89    4      |
| 1     9    b57     | 4     6     8      | 3    c57    2      |
| 4     3     8      | 25    27    9      | 6     1     57     |
*--------------------------------------------------------------*

The puzzle then solves easily. If you are not familiar with these solving techniques I can explain them in more detail.

Alternatively here are links to two excellent teaching sites, which discuss these techniques and a whole lot of others.

http://www.sudokuwiki.org/Strategy_Families

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

PS. Just rechecking my solution I noticed that you only need the Skyscraper plus a pointing pair in r6c78 which removes the 7 from r6c5 to solve the puzzle.

Leren
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