The New Sudoku Players' Forum

[Bluewaterpig]

I’ve been solving Sudoku puzzles for a few years now, and this is my first attempt at a puzzle labeled as “demanding”. I know most of the basic strategies, but I’m pretty positive that the solution for this one will come from an advanced strategy that I don’t know about. This will probably be pretty easy for anyone who’s even slightly advanced.

Can someone find even just one more answer and then tell me the strategy they used? I’ll be delighted to learn the method that unlocks the next number...
http://i1280.photobucket.com/albums/a484/bluewaterpig/7F6EC401-4FD6-4410-B0DF-29AEE3A5B056_zpsqa0bf306.jpeg

[Leren]

Code: Select all

*-----------*
|...|...|.3.|
|47.|...|...|
|9..|.1.|...|
|---+---+---|
|..8|1..|.2.|
|2..|5..|..7|
|..3|.6.|.1.|
|---+---+---|
|..5|.7.|..2|
|...|..5|..9|
|..7|2.8|..1|
*-----------*

This is actually a very easy puzzle. After marking off the clues and looking for naked and hidden singles, you end up here, which is close to what you have pencilled in on your diagram.

Code: Select all

*-------------------------------------------------------*
|*568 *568 126 | 4789 2489-5 479 | 124678-5 3     468-5 |
| 4    7   12  | 3   #258    6   | 1258     9     58    |
| 9    3   26  | 478  1      47  | 245678   45678 4568  |
|--------------+-----------------+----------------------|
| 567  456 8   | 1    49     479 | 4569     2     3     |
| 2    1   9   | 5    48     3   | 468      468   7     |
| 57   45  3   | 4789 6      2   | 4589     1     458   |
|--------------+-----------------+----------------------|
| 368  689 5   | 49   7      1   | 3468     468   2     |
| 1    2   4   | 6    3      5   | 78       78    9     |
| 36   69  7   | 2    49     8   | 3456     456   1     |
*-------------------------------------------------------*

There is a Box/Row intersection (pointing pair) of 5's in Box 1 in the cells marked *. As these are the only two 5's in Box 1, one of them must be True, so you can eliminate the other three 5's in Row 1, as I've indicated.

The puzzle then just solves with a cascade of singles, the first of which is that r2c5 must be 5 as it is the only 5 in Column 5 and Box 2.

If you really don't know about intersection removals, let me know and I'll give you some links to some excellent teaching sites.

Leren

[eleven]

Hi Bluewaterpig,

what a trash site you posted in your link! i have to wait a minute (what are they doing in that time?) to get some advertisements and your puzzle.
Please look at Leren's post, how to post a puzzle, or attach a photo here.

For that puzzle you don't have to fill in any candidates. Just look for pairs (they are well hidden).

[Leren]

I'd have agree with elevens comments. It was quite difficult to bring up your puzzle and I did a security check afterwards, in case some malware had been installed on my PC. Leren

[Bluewaterpig]

First...thanks for the replies.

I’ve looked up the concept of “pointing pairs”. This was a strategy I was already familiar with.

I still don’t understand the significance of the pointing pair of 5s in my box 1...even though they’re present, 5s can still occur across the bottom row of box 3, so how does that help me solve anything?

[Pat]

I still don’t understand the significance of the pointing pair of 5s in my box 1

how does that help me solve anything?

as Leren said,
excluding 5 at r1c5
solves the 5 for b2
(or equally, for c5)

you can eliminate the other 5s in Row 1

---r2c5 must be 5
as it is the only 5 in Column 5 and Box 2.

[Leren]

I've added a # to r2c5 in my PM. If you look at the diagram closely, when the 5 is removed from r1c5, 5 is the only one left in Column 5 or Box 2. That's a hidden single, so it must be 5.

When you mark that off, at least one other single will appear. One I can see is that r2c9 is not 5, so it's 8. When you mark that off, at least one other single will appear ...... and so on until the puzzle is fully solved.

Leren