markb wrote:"I have got as far as the fiendish puzzles.....

...but can't finish one.

When you come to a stand still, fill in all possible candidates in each unsolved cell. Read the tutorials at

Simple Sudoku,

Sadman Sudoku and

Sudoku Susser (You have to download Susser to get the PDF tutorial. You don't have to install it -- but all three of these software apps are very good learing tools.) Read these forums, work through examples. To search in this forum, use GOOGLE, click on advanced search and restrict the domain to sudoku.com.

markb wrote:I get to the stage were I have to guess at one a number going into 1 of 2 boxes. I thought that you could always get the next number through logic?? It is only when putting the last few (say 4 - 6) numbers in that the mistake becomes apparent.

So my questions are 'Can you always get the next number through logic?'. and 'Where can I learn the technique?'. "

It is always possible for each and every Sudoku to be solved by logic and there are always many paths to the solution. There is no one technique, no magic bullet. It is also possible for a puzzle to be beyond the skills of any individual person. It is not possible to create a Sudoku that requires guessing anymore than you can create a crossword puzzle that requires guessing. Having mastered arithmetic, a student shouldn't be frustrated in not being able to solve problems that require calculus.

markb wrote:Puzzle is

**9|8*7|**2

***|312|8**

2*8|6*9|***

854|723|**1

**1|468|325

623|591|748

**2|176|4*3

**7|285|***

1**|934|2**

Here's your puzzle:

- Code: Select all
` . . 9 | 8 . 7 | . . 2 `

. . . | 3 1 2 | 8 . .

2 . 8 | 6 . 9 | . . .

-------+-------+------

8 5 4 | 7 2 3 | . . 1

. . 1 | 4 6 8 | 3 2 5

6 2 3 | 5 9 1 | 7 4 8

-------+-------+------

. . 2 | 1 7 6 | 4 . 3

. . 7 | 2 8 5 | . . .

1 . . | 9 3 4 | 2 . .

The candidates lists:

- Code: Select all
` 345 1346 9 | 8 45 7 | 156 1356 2 `

457 467 56 | 3 1 2 | 8 5679 4679

2 1347 8 | 6 45 9 | 15 1357 47

-------------------+-------------------+-------------------

8 5 4 | 7 2 3 | 69 69 1

79 79 1 | 4 6 8 | 3 2 5

6 2 3 | 5 9 1 | 7 4 8

-------------------+-------------------+-------------------

59 89 2 | 1 7 6 | 4 589 3

349 3469 7 | 2 8 5 | 169 169 69

1 68 56 | 9 3 4 | 2 5678 67

Look in box 9. Row 8 columns 7,8,9 form a naked triple [169]. This excludes 1s, 6s and 9s from the rest of box 9 and from the rest of row 8. Nothing but singles is required after this.