dailysudoku.com

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

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.

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

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.

Mesmin · Joined: 01 May 2007 Posts: 12 Location: Ontario

Mogulmeister · Joined: 03 May 2007 Posts: 1151

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

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

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

Marty R. · Posted: Thu May 17, 2007 3:33 pm Post subject:

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.