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stewsbetty



Joined: 16 May 2007
Posts: 2
Location: quesnel, bc

PostPosted: Wed May 16, 2007 5:16 am    Post subject: want to improve Reply with quote

hi i am new here. i have been doing sudoku for about year and half. i have learned some logic ideas through working puzzles but seem to have reached a dead end. i have tried reading some of the logic tips in these forums but find it hard when it is not related to a specific puzzle. when i reach an impasse with a puzzle i just give in and guess and check. so will someone please help me with the following. i followed someones link to brainbashers and tried this very hard. i am stuck here.

7 9 12 | 25 56 4 | 13 8 136
5 14 124 |8 3 26 | 7 9 16
6 8 3 | 7 1 9 | 2 5 4
1 2 5 | 4 7 8 | 6 3 9
8 346 46 | 23 9 26 | 5 1 7
9 36 7 | 35 56 1 | 8 4 2
2 7 9 | 1 8 35 | 4 6 35
4 16 168 | 9 2 35 | 13 7 1358
3 5 18 | 6 4 7 | 9 2 18

so if anyone could give me a personalized lesson it would be greatly appreciated.
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David



Joined: 02 Jun 2006
Posts: 58
Location: Bedford, UK

PostPosted: Wed May 16, 2007 8:25 am    Post subject: Reply with quote

Well, Mrs Betty, I can tell you how to solv it, but you may have to do some 'research' on the two techniques I will give you.

First, if you concentrate on the four cells at r8c3,9 and r9c3,9 you will see that you have the following;

168 1358
18 18

The candidates 18 in all four cells form a 'deadly pattern' in that if these were the only candidates left, you would have two possible solutions to the puzzle (not allowed !). This is in fact a type 4 unique rectangle and allows you to eliminate the candidate 1 in r8c3 and r8c9.

Having got rid of the 1 in r8c3 leaves you with only two possible cells in block7 with a '1'. This allows you to do some simple 'colouring' on 1 as follows;

r2c2-r8cc2-r9c3-r9c9 and this eliminates the '1' inr2c9 to leave a '6'.

The puzzle collapses from there.
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Mesmin



Joined: 01 May 2007
Posts: 12
Location: Ontario

PostPosted: Wed May 16, 2007 1:53 pm    Post subject: Reply with quote

Code:

+-----------+----------+-----------+
| 7 9   12  | 25 56 4  | 13 8 136  |
| 5 14  124 | 8  3  26 | 7  9 16   |
| 6 8   3   | 7  1  9  | 2  5 4    |
+-----------+----------+-----------+
| 1 2   5   | 4  7  8  | 6  3 9    |
| 8 346 46  | 23 9  26 | 5  1 7    |
| 9 36  7   | 35 56 1  | 8  4 2    |
+-----------+----------+-----------+
| 2 7   9   | 1  8  35 | 4  6 35   |
| 4 16  168 | 9  2  35 | 13 7 1358 |
| 3 5   18  | 6  4  7  | 9  2 18   |
+-----------+----------+-----------+



Alternate methods with out coloring:

There's also a finned x-wing in rows 1 and 9, on the number 1. Either it's an x-wing on r1c3 r1c9 r9c3 r9c9, or the 1 belongs in r1c7. Both options mean that the 1 cannot be in r2c9. Leaving just the 6. The puzzle opens up from there.

Another potential solution is a Unique Rectangle on 35, in r7c7 r7c9 r9c7 r9c9. To avoid the "deadly pattern", this UR forces either a 1 or an 8 into r8c9 which acts as a "virtual" naked pair with the 18 in r9c9. Again this eliminates the 1 from r2c9 (as well as the 1 from r8c7 and r1c9).

I find that Brainbashers heavily uses URs as a solving technique.

Brainbashers has some excellent resources for learning techniques. Whenever you start a puzzle on, you should have a link on the right of the puzzle that shows you what the potential techniques required to solve the puzzle. Each technique is a clickable link which gives an explanation and example of the method.

Note that the "show potential techniques" link does not appear when you manually type in a puzzle or load from a saved spot.
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Mogulmeister



Joined: 03 May 2007
Posts: 1151

PostPosted: Wed May 16, 2007 3:53 pm    Post subject: Reply with quote

Betty,

I don't want to confuse you further but these examples show that in most sudoku puzzles there is more than one way home. So far you have heard about Unique rectangles and finned x-wings etc.

Another technique is called x-y chains or "golden chains". This technique is useful when you have a good number of bivalue squares (squares with only 2 candidates). Look at this picture below:



I have coloured two squares in green- these are the "pincers" or ends of the xy chain they both contain 1 and these 1's can both "see" the 1 in our target cell r2c2 (coloured blue).

So how does the chain link up ?

We leave the 1 in r1c3 looking at the target and then use the 2 in r1c3. This links to the 2 in r1c4 so that is used up. xx to the 5 in r1c4.

We now take the 5 from r1c4 to link to the 5 in r6c4. xx to the 3 in r6c4 and link to the 3 in r6c2. xx to the 6 in r7c2.

We have arrived at the other pincer - the remaining 1 completes the loop.

Because both 1's can see r2c2 that 1 is eliminated.

A bit long winded but if you trace it through you will see it takes much less time to do than talk about !! Smile
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stewsbetty



Joined: 16 May 2007
Posts: 2
Location: quesnel, bc

PostPosted: Thu May 17, 2007 4:17 am    Post subject: thanks a bunch Reply with quote

hello i am pretty new at this posting business so sorry about the crappy puzzle layout. i really appreciate the ideas. i think i caught on to the xy chains idea. i will have to review the other ones more closely. i think i will go back to brainbashers and look at what suggestions/lessons that they had next to that puzzle. thanks for the help and if i anyone can tell me how to insert a puzzle in here so it is laid out properly i'm sure everyone would appreciate it. thanks again. beth
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Thu May 17, 2007 3:33 pm    Post subject: Reply with quote

Beth,

There are two good ways to post a properly aligned grid.

If you are doing a puzzle (regardless of puzzle source) online on this site, all you have to do is click the "Ascii" button to the right of the grid. Then follow the instructions in the pop-up window to copy and paste the grid into the message box.

Otherwise, type the grid into Notepad, which uses a fixed xx font, or into a word processing program, and choose a font that uses a fixed xx, such as Courier New. Proofread the grid before posting. Select (highlight) the grid and copy it (Ctrl+C). In the forum message box, click "Code", then paste (Ctrl+V) the grid to the right of the Code tag. Click "Code" again which inserts the tag at the end of the grid.

A properly aligned grid makes it easier for people to analyze your position and may well get you a quicker response.

This is an example of a grid which was first typed into Notepad. It takes less time than it looks like, as once you establish the maximum number of spaces per cell, you get into a rhythm and it takes less than five minutes.


Code:

-------------------------------------------------------------------
|23569  2369   1      |259    8      7      |2356   356    4      |
|23569  23689  2359   |1      24     49     |235678 35678  2358   |
|4      28     7      |25     3      6      |9      1      258    |
-------------------------------------------------------------------
|1239   4      239    |289    126    5      |368    3689   7      |
|123579 123579 6      |289    12     39     |4      3589   13589  |
|8      139    359    |7      146    349    |356    2      1359   |
-------------------------------------------------------------------
|27     5      8      |3      9      1      |27     4      6      |
|139    139    4      |6      7      2      |358    3589   3589   |
|23679  23679  239    |4      5      8      |1      379    239    |
-------------------------------------------------------------------
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