please help with puzzle 187 - tough from sudoku for dummies

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

please help with puzzle 187 - tough from sudoku for dummies

Postby lerfalds » Sat Mar 11, 2006 2:40 am

I have worked on this puzzle for hours. I just tried to learn coloring, but it didn't seem to work. I tried coloring the 3's starting with r3c5 green, then r3c6 and r5c5 blue, etc. Maybe I didn't fully understand it. Please help - this puzzle is driving me crazy. Thanks!!

6 3 1 7 9 5 4 8 2
9 8 5 1 4 2 6 3 7
4 2 7 86 36 38 5 9 1
138 16 2 4 7 38 9 5 36
5 9 36 2 36 1 8 7 4
38 7 4 68 5 9 2 1 36
2 16 68 9 18 7 3 4 5
13 4 38 5 18 6 7 2 9
7 5 9 3 2 4 1 6 8
[/code]
lerfalds
 
Posts: 2
Joined: 10 March 2006

Postby Chessmaster » Sat Mar 11, 2006 3:51 am

is this from sudoku for dummies 1 or 2
Chessmaster
 
Posts: 191
Joined: 21 December 2005

Postby emm » Sat Mar 11, 2006 4:07 am

Here are the 3s – there are two separate chains Aa and Bb – they are not connected and no 3s can be eliminated.
Code: Select all
 .  .  .  | .  .  . |  .  .  .
 .  .  .  | .  .  . |  .  .  .
 .  .  .  | .  3A 3a|  .  .  .
----------+---------+--------
 3  .  .  | .  .  3A|  .  .  3B
 .  .  3A | .  3a . |  .  .  .
 3B .  .  | .  .  . |  .  .  3b
----------+---------+--------
 .  .  .  | .  .  . |  .  .  .
 3A .  3a | .  .  . |  .  .  .
 .  .  .  | .  .  . |  .  .  .


This puzzle has a classic BUG pattern – every number appears exactly twice in every row, column and box – except for one cell = r4c1. If each number was exactly twice in the grid then you would have two possible solutions. Assuming that this is a Sudoku with a unique solution, you have to place the only number that prevents the BUG pattern => r4c1 = 3

Code: Select all
*--------------------------------------------------*
 | 6    3    1    | 7    9    5    | 4    8    2    |
 | 9    8    5    | 1    4    2    | 6    3    7    |
 | 4    2    7    | 68   36   38   | 5    9    1    |
 |----------------+----------------+----------------|
 | 138* 16   2    | 4    7    38   | 9    5    36   |
 | 5    9    36   | 2    36   1    | 8    7    4    |
 | 38   7    4    | 68   5    9    | 2    1    36   |
 |----------------+----------------+----------------|
 | 2    16   68   | 9    18   7    | 3    4    5    |
 | 13   4    38   | 5    18   6    | 7    2    9    |
 | 7    5    9    | 3    2    4    | 1    6    8    |
 *--------------------------------------------------*

Alternatively, there is an XY wing at r4c6, r4c9 and r6c4 that eliminates the 6 from r6c9.
If you have two cells in a group that share a candidate - r4c6 (XY) and r4c9 (XZ) – and a third cell with the unshared candidates – r6c4 (ZY) – also shares a group with one of those cells, then no cell that ‘sees’ both Zs can be Z and no cell that 'sees' both Ys can be Y. In this case r6c9 <> 6.

This can be explained as a forcing chain
r4c6=3 => r4c9=6 => r6c9<>6
r4c6=8 => r6c4=6 => r6c9<>6
emm
 
Posts: 987
Joined: 02 July 2005

Postby QBasicMac » Sat Mar 11, 2006 4:31 am

If r5c3=3 then r6c1=8. That leaves 6 in r5c5 and r6c4 - impossible.
Therefore r5c3=6
QBasicMac
 
Posts: 441
Joined: 13 July 2005

Postby tarek » Sat Mar 11, 2006 9:53 am

This solves it.
Code: Select all
*-----------------------------------------------*
| 6    3    1   | 7    9    5   | 4    8    2   |
| 9    8    5   | 1    4    2   | 6    3    7   |
| 4    2    7   | 68   36   38  | 5    9    1   |
|---------------+---------------+---------------|
| 138  16   2   | 4    7    38  | 9    5    36  |
| 5    9    36  | 2    36   1   | 8    7    4   |
| 38   7    4   | 68   5    9   | 2    1    36  |
|---------------+---------------+---------------|
| 2    16   68  | 9    18   7   | 3    4    5   |
| 13   4    38  | 5    18   6   | 7    2    9   |
| 7    5    9   | 3    2    4   | 1    6    8   |
*-----------------------------------------------*
Eliminating 6 From r6c9 (3 & 8 in r4c6 form an XY wing with 6 in r4c9 & r6c4)

Tarek
User avatar
tarek
 
Posts: 2699
Joined: 05 January 2006

THANKS!!

Postby lerfalds » Sat Mar 11, 2006 8:14 pm

Thanks everyone for the help!!

Chessmaster - This puzzle is from Dummies 1.

EM - I think I finally understand xy wing. Thanks!!

Lerfalds
lerfalds
 
Posts: 2
Joined: 10 March 2006

Postby tommy » Mon Mar 13, 2006 10:10 pm

hello anyone and everyone.

I am a newbie at this sudoku game and i love it.

I can do the easy puzzles, the tricky ones , and most tough ones.

I even have completed a few of the diabolical ones.

I have been using the sudoku for dummies and i clearly see i need to advance my skills. I would very much appreciate any help. I found this sight and by reading this forum I can see i have a lot to learn.

I want to be able to solve the more difficult puzzles using logic and not resorting to a guess.

tommy
tommy
 
Posts: 8
Joined: 13 March 2006


Return to Help with puzzles and solving techniques