The New Sudoku Players' Forum

[gwandless]

Here is the puzzle :

1-- -8- 9--
--6 --5 -7-
-9- --4 -1-

-4- 7-- 85-
-1- -58 ---
865 --2 -3-

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

I know the next "step" is to put a 1 in box 6 at r4c9 but I can't figure out why.

Can someone explain the logic.

The reason I know what the next step is from sudokuhints.com.

[CathyW]

I'm not so sure that would necessarily be the next 'logical' step. There are many roads that lead to Rome, as they say. I can't personally see how you can place 1 at r4c9 immediately.

You haven't posted your candidate list so we don't know what you've eliminated.

Anyway, basic steps (pairs and locked candidates) gets you to here:

Code: Select all

 *-----------------------------------------------------------*
 | 1     35    2347  | 236   8     367   | 9     24    356   |
 | 24    38    6     | 19    19    5     | 24    7     38    |
 | 2357  9     2378  | 236   367   4     | 56    1     3568  |
 |-------------------+-------------------+-------------------|
 | 239   4     239   | 7     36    1369  | 8     5     1269  |
 | 2379  1     2379  | 3469  5     8     | 246   24    269   |
 | 8     6     5     | 149   19    2     | 147   3     179   |
 |-------------------+-------------------+-------------------|
 | 3459  7     349   | 8     34    139   | 125   6     125   |
 | 469   2     489   | 5     467   1679  | 3     89    17    |
 | 3569  358   1     | 369   2     3679  | 57    89    4     |
 *-----------------------------------------------------------*


I would then use the Unique Rectangle of {19) in r2c45 and r6c45. Assuming there is a unique solution (and there must be if it's a Pappocom puzzle!), you can place 4 at r6c4.

That leaves only one place for a 1 in column 4. A few singles later and you can indeed place 1 in r4c9. The rest is also singles, some naked some hidden.

[gwandless]

Thanks Cathy.

[Animator]

CathyW, good work but you missed a (simple) elimination...

The number 1 in box 8 is locked in column 6.
This means that r4c6 cannot be the number 1.
And this leaves a hidden single on row 4. Namely the number 1 in r4c9.

[Hud]

Cathy, that's the same road I took. My first placement was the unique 4 and the second was the 1 in question. I didn't try it without the 4 so maybe it could have been done that way as well.

No rain here since Oct 18.

[CathyW]

Yup - quite right Animator, of course! Can't believe I missed the locked 1s in box 8 having made the other eliminations. Perhaps the UR was 'easier' to see at that point since Hud went that way too!

[gwandless]