## Another hard that's got me stumped

Advanced methods and approaches for solving Sudoku puzzles

### Another hard that's got me stumped

I got pretty far and I'm surprised I'm stuck this far into it:

* 3 4 * * * * 9 *
* 1 * 9 * 7 3 * *
9 * * * 3 * * * 1

3 8 7 4 1 6 9 2 5
* 2 * 8 7 9 6 4 3
6 4 9 3 5 2 1 7 8

4 * * * * * * 3 *
* * 8 7 * 3 * 1 *
* 9 3 * * * 2 8 *
Loren Pechtel

Posts: 21
Joined: 06 June 2005

Here's a possible next step, courtesy of my deductive solver:

Code: Select all
`* 2 squares in block 3 form a simple locked pair.  The following squares share possibilities <56>:   R2C8   R3C8  Thus, possibilities <56> can be removed from  the rest of the block.   R1C1 - removing <5> from <578> leaving <78>.   R1C7 - removing <5> from <4578> leaving <478>.   R1C3 - removing <6> from <267> leaving <27>.   R1C6 - removing <6> from <246> leaving <24>.`

Posts: 81
Joined: 10 June 2005

Look carefully at row 3...there is a pair...if you identify this you can eliminate other numbers from the rest of the row and place a number in box 1...
Arnie

Posts: 49
Joined: 19 May 2005

Arnie wrote:Look carefully at row 3...there is a pair...if you identify this you can eliminate other numbers from the rest of the row and place a number in box 1...

Yeah, I guess there is. It didn't sink in until you pointed it out.

Incidently, in regards to post #2, I saw the 5,6 in block 3 but it didn't give me anything useful.
Loren Pechtel

Posts: 21
Joined: 06 June 2005

Strangely enough I'm still stuck despite the progress.

* 3 4 * * * * 9 *
* 1 * 9 * 7 3 * *
9 7 * * 3 * * * 1

3 8 7 4 1 6 9 2 5
1 2 5 8 7 9 6 4 3
6 4 9 3 5 2 1 7 8

4 * 1 * * * * 3 *
2 * 8 7 * 3 * 1 *
7 9 3 * * * 2 8 *

Columns 1, 2, 3 & 8 are all restricted to a pair of #'s although this only eliminates some options in box 3. There's also a few #'s eliminated in row 3 but that doesn't do me any good either.
Loren Pechtel

Posts: 21
Joined: 06 June 2005

Look carefully at row 9.

It contains a pair of two numbers. What does it mean for the other cells on that row?

When you are done with that you should take a good look at box 8
Animator

Posts: 469
Joined: 08 April 2005

Animator wrote:Look carefully at row 9.

It contains a pair of two numbers. What does it mean for the other cells on that row?

When you are done with that you should take a good look at box 8

That knocked out a couple of numbers but I don't see it changing the situation in box 8.

However I just noticed a wrong pencil mark in box 2. I think I need to recheck all my penciling.
Loren Pechtel

Posts: 21
Joined: 06 June 2005

It does change the situation in box 8.

Now you should have two pairs on row 9. And one of those two is in box 8.

And in box 8 there is a cell that has one of those two numbers and another number. Obviously it can't have the one that is part of the pair...
Animator

Posts: 469
Joined: 08 April 2005

Animator wrote:It does change the situation in box 8.

Now you should have two pairs on row 9. And one of those two is in box 8.

And in box 8 there is a cell that has one of those two numbers and another number. Obviously it can't have the one that is part of the pair...

Duh! Why did I miss that 5?!?!
Loren Pechtel

Posts: 21
Joined: 06 June 2005

When you talk about pairs in cells do you mean that the same pair of numbers can go in one/two cells?
Frazzle

Posts: 4
Joined: 10 June 2005

There are two possibilities when I talk about pairs:

* first one is that there are two cells, with only two possible candidates and those candidates are the same.

* second case, there are two numbers that can go in two cells and those are the only cells for those two numbers (this one can have more then two candidates in the cells. (the cells has to be the same for both numbers).

An example for the first would be the 4, 6 pair on row 9. An example for the second explenation would be the 1, 5 pair on row 9
Animator

Posts: 469
Joined: 08 April 2005