Is This A Bug In 'Simple Sudoku 4.1w'?

Spok

Here is a puzzle I have been solving.

This is the starting grid:

*-----------*
|.13|8..|5..|
|...|.1.|...|
|26.|...|3..|
|---+---+---|
|6.9|..8|...|
|7..|.4.|..6|
|...|7..|9.8|
|---+---+---|
|..5|...|.13|
|...|.7.|...|
|..7|..9|62.|
*-----------*

I have got this far with it, and all the numbers I have put in so far are correct:

*-----------*
|913|8..|5..|
|57.|.1.|...|
|26.|.9.|3.1|
|---+---+---|
|6.9|..8|...|
|78.|94.|..6|
|...|7..|9.8|
|---+---+---|
|.95|...|713|
|.26|.7.|...|
|..7|..9|62.|
*-----------*

Being stuck, I put the above position into 'Simple Sudoku' to have a look at the candidates.

Simple Sudoku produces these candidates:

*--------------------------------------------------------------------*
| 9 1 3 | 8 26 2467 | 5 467 247 |
| 5 7 48 | 2346 1 2346 | 248 4689 249 |
| 2 6 48 | 45 9 457 | 3 478 1 |
|----------------------+----------------------+----------------------|
| 6 345 9 | 1235 235 8 | 124 3457 2457 |
| 7 8 12 | 9 4 1235 | 12 35 6 |
| 134 345 124 | 7 2356 12356 | 9 345 8 |
|----------------------+----------------------+----------------------|
| 48 9 5 | 246 268 246 | 7 1 3 |
| 1348 2 6 | 1345 7 1345 | 48 4589 459 |
| 1348 34 7 | 1345 358 9 | 6 2 45 |
*--------------------------------------------------------------------*

Column C has 4 missing numbers (1 2 4 8). The top left mini-grid has two missing numbers (4 8).

Simple Sudoku correctly indicates that only 4 & 8 can go in C2 and C3. So only the numbers 1 & 2 are left to go in C5 and C6.

Why, then, does Simple Sudoku suggest that the candidates for C6 are (1 2 4). If C6 were to be 4 (which it isn't) then the top left mini-grid would be without a 4.

Is this a bug?

Any help would be appreciated.

Spok.

angusj · Site Admin

No, this is not a bug.

The only automatic candidate eliminations that SS does is remove candidates from related cells whenever a 'Big Number' is assigned.

For example, if a 1 is assigned to cell R1C1, then all cells in Row1, Column1 and Box1 would have their candidate 1 removed automatically. (This kind of candidate removal is so elementary that I presume most people would find it as boring as I do.) However, all other candidate eliminations are left to you, the human solver, otherwise there'd be almost no challenge left, and no fun in solving Sudoku.

To highlight this point - you'll notice that cell R6C3 (the one you're questioning) still contains a candidate 4. It hasn't been automatically removed because there's still no 4 assigned to any cell in its related row, column or box.

Spok

Angus,

Thanks for that.

I have only recently dicovered this brilliant program. It is a fantastic training tool, with its hints and display in the Status Bar of 'why' it is suggesting a particular move.

And it's free!

Thanks very much for this marvelous resource.

Spok.