## Yikes!

Advanced methods and approaches for solving Sudoku puzzles

### Yikes!

I have just started playing Sudoku this week. One word:wow!

Anyway, today I tackled my first hard puzzle from this link:

http://www.dailysudoku.co.uk/sudoku/index.html

xxx xxx x89
7xx xx2 3xx
x1x xx3 2xx

8xx x36 7x2
xxx 9x5 xxx
9x1 28x xx3

xx9 3xx x5x
xx5 6xx xx4
28x xxx x3x

Here's what I came up with so far:

xxxxxxx89
79xxx23xx
x1xx9327x
854136792
xxx9x5xxx
9x128x5x3
xx932xx5x
xx56xxx24
28xxxxx3x

When I asked for a hint from the Draw(er), a 7 was filled into the last row

287xxxx3x

So my question is, why a 7?

Thanks!
jammaj, who needs to read up on X-wings and Swordfishes and who knows what all!!!!!
jammaj

Posts: 2
Joined: 25 June 2005

"Disjoint subset".

In column 3, there are three cells (2,3)(3,3)(9,3) that have candidates of only 6, 7 or 8. Three cells, with only three candidates, means each cell takes a candidate, so you can eliminate those candidates for other cells in the column.

After that, there's only one cell in the column that can be a 7.

Tricky, but true!
Last edited by simes on Sun Dec 11, 2011 9:47 am, edited 1 time in total.
simes

Posts: 324
Joined: 11 March 2005
Location: UK

Many thanks, Simes! Tricky, but true works for me!!!

Also, thanks for the Sudoku tutorial on your website!

Enjoy!
jammaj

simes wrote:"Disjoint subset".

In column 3, there are three cells (2,3)(3,3)(9,3) that have candidates of only 6, 7 or 8. Three cells, with only three candidates, means each cell takes a candidate, so you can eliminate those candidates for other cells in the column.

After that, there's only one cell in the column that can be a 7.

Tricky, but true!

Simes
http://www.simes.clara.co.uk/programs/sudoku.htm
jammaj

Posts: 2
Joined: 25 June 2005