Number Groups and "very hard"

Advanced methods and approaches for solving Sudoku puzzles
Animator wrote:you reached a point where you had a cell without candidates. (somewhere else in the grid I guess in column 3 (that's where I found such a cell)

Animator, help me see what I'm missing in column 3. With 261 placed in column 9 in block 6, I have the following for column 3: {56} {56} {289} [3] [1] [7] [4] {28} {89}. What did I miss to get an empty cell in that column?
scrose

Posts: 322
Joined: 31 May 2005

Roz wrote:I'll stick to the tried and tested ways in future!

There's nothing wrong with using trial-and-error. What you did quickly led to the solution. Oftentimes, when I am stuck, I'll manipulate a puzzle with trial-and-error to get back on track. Then I'll return to the point where I was stuck and, with the help of knowing where a few numbers should or shouldn't be, try and figure out how it can be solved by logic.

I think Animator and I were just trying figure out if you had discovered something that we had missed. I hope our posts helped you see how this puzzle can be solved by logic. Please don't refrain from sharing your opinions and reasoning in the future. Like joolslee said, this kind of discussion helps others who are using the same line of reasoning.
scrose

Posts: 322
Joined: 31 May 2005

scrose wrote:There's nothing wrong with using trial-and-error. What you did quickly led to the solution. Oftentimes, when I am stuck, I'll manipulate a puzzle with trial-and-error to get back on track. Then I'll return to the point where I was stuck and, with the help of knowing where a few numbers should or shouldn't be, try and figure out how it can be solved by logic.

I know there's nothing wrong with trial and error, but it's wrong when unintentional, and it was. ;-)

scrose wrote:I think Animator and I were just trying figure out if you had discovered something that we had missed. I hope our posts helped you see how this puzzle can be solved by logic. Please don't refrain from sharing your opinions and reasoning in the future. Like joolslee said, this kind of discussion helps others who are using the same line of reasoning.

Yes I realise that, and I'm sorry for how I reacted, but I think we all react "On the hoof" at times. I wont stop enjoying Sudoku or posting to the forums at times, don't worry!
Roz

Posts: 34
Joined: 25 May 2005

scrose wrote:Animator, help me see what I'm missing in column 3.

It's not an immediate error... (there might be one but I haven't found it).

I was able to reach this grid with r6c9 = 1: (you can fill in some more numbers too but they are irrelevant)
4 * * | * 9 1 | * * 8
3 * * | 2 * 8 | * 1 *
7 1 * | * 5 3 | * 6 *
-----------------------
* * 3 | 1 * 7 | 9 * *
* * 1 | * * 9 | 7 * *
* 9 7 | 5 * 2 | 3 * 1
-----------------------
9 6 4 | * 1 5 | 8 2 *
1 * * | 9 * 4 | 6 * 5
5 * * | * 2 6 | 1 9 4

With this grid there is only one place for the number 8 in box 1, r3c3.

And the only candidate for r9c3 is 8. This means that you have the number 8 twice in column 3. (or the number 8 and an empty cel).

I'm pretty sure there are other ways to show that this grid is impossible... as in, at one pointed I reached an error in column 1 but I no longer have that grid.
Animator

Posts: 469
Joined: 08 April 2005

Animator wrote:It's not an immediate error... (there might be one but I haven't found it).

Okay, whew. Thanks, I thought I was missing something glaringly obvious.
scrose

Posts: 322
Joined: 31 May 2005

Previous