## Solve the impossible

Post the puzzle or solving technique that's causing you trouble and someone will help

### Solve the impossible

[I'm stuck. I just need to know which one is the next move (digit). Thanks. Gracias

+------+--------+-------+
3 _ 1 2 _ _ _ _ 7

_ _ _ 1 _ 7 _ _ _

7 _ 6 9 3 4 5 1 _
+-------+-------+--------+
_ 7 _ 4 _ 9 1 8 _

9 _ _ _ 2 1 7 _ 4

_ 1 _ 8 7 3 _ 5 _
+-------+-------+---------+
_ _ 9 _ 4 _ 3 7 1

_ _ _ 7 _ 2 8 _ 5
_ _ 7 3 _ 8 _ _ 6
+-------+-------+---------+
This is a pappocom puzzle from sudoku web page
Javier Cia

Posts: 10
Joined: 02 January 2006

First of all, here are the puzzle (in a legible form) and the candidate grid.

Code: Select all
` 3 . 1 | 2 . . | . . 7  . . . | 1 . 7 | . . .  7 . 6 | 9 3 4 | 5 1 . -------+-------+------  . 7 . | 4 . 9 | 1 8 .  9 . . | . 2 1 | 7 . 4  . 1 . | 8 7 3 | . 5 . -------+-------+------  . . 9 | . 4 . | 3 7 1  . . . | 7 . 2 | 8 . 5  . . 7 | 3 . 8 | . . 6      3   4589     1 |   2  568  56 |   469    469     7   2458  24589  2458 |   1  568   7 |  2469  23469  2389      7     28     6 |   9    3   4 |     5      1    28 --------------------+--------------+-------------------    256      7   235 |   4   56   9 |     1      8    23      9   3568   358 |  56    2   1 |     7     36     4    246      1    24 |   8    7   3 |   269      5    29 --------------------+--------------+-------------------   2568   2568     9 |  56    4  56 |     3      7     1    146    346    34 |   7  169   2 |     8     49     5   1245    245     7 |   3  159   8 |   249    249     6 `

I suspect that you ought to read about locked candidates, pairs and triples elsewhere on this forum. You'll have to find quite a few in order to make the next move. After that, you'll have to find some more!

Here are the eliminations that lead up to the first move:

Code: Select all
`The value 2 in Box 7 must lie in Row 7.- The moves r9c1:=2 and r9c2:=2 have been eliminated.The values 2 and 8 occupy the cells r7c1 and r7c2 in some order.- The moves r7c1:=5, r7c1:=6, r7c2:=5 and r7c2:=6 have been eliminated.The value 5 in Box 8 must lie in Row 7.- The move r9c5:=5 has been eliminated.The value 6 in Box 8 must lie in Row 7.- The move r8c5:=6 has been eliminated.The values 3, 4, 5, 6 and 9 occupy the cells r1c2, r2c2, r5c2, r8c2 and r9c2 in some order.- The moves r1c2:=8, r2c2:=2, r2c2:=8 and r5c2:=8 have been eliminated.The cell r1c5 is the only candidate for the value 8 in Row 1.`

I'll leave the rest to you.
rubylips

Posts: 149
Joined: 01 November 2005

rubylips wrote:The value 2 in Box 7 must lie in Row 7.
- The moves r9c1:=2 and r9c2:=2 have been eliminated.

You meant Box 9.

Hope that didn't confuse the OP. Otherwise, good, useful explanation!

(Unless it is me that is confused)

Mac
QBasicMac

Posts: 441
Joined: 13 July 2005

QBasicMac wrote:You meant Box 9.

Check across Row 7 - all the 2s are in Box 7, so it's safe to eliminate the 2s in Box 7 outside Row 7.
rubylips

Posts: 149
Joined: 01 November 2005

There are two ways to look at it:
• Box 9: all the candidates for number 2 are on row 9.
• Row 7: all the candidates for number 2 on row 7 are in box 7.
Both views lead to the conclusion that r9c1 nor r9c2 can be the number 2.

Changing the wording of rubylips post could make more sense...
(From: 'The value 2 in box 7 must lie in Row 7' to: 'The value 2 in Row 7 must lie in box 7')
Animator

Posts: 469
Joined: 08 April 2005

Thanks for the info, rubylips and animator.

Correct. I was confused by the wording that animator pointed out, but might have eventually got it if it weren't for the other path.

Mac

By the way, the reason I looked at the post at all is that I was favorably impressed by the reasonable details you provided. There are a few people here who would respond with the equivalent of "You need to try to get as smart as I am by studying up on locked candidates - see [reference to general work]" Sometimes the arrogance of such posts is tempered by a vague reference to some part of the grid. They don't have any intention of helping the person with the problem, just trying to show off. It is refreshing to see people actually trying to help.
QBasicMac

Posts: 441
Joined: 13 July 2005

### solve the impossible

Got it!!!
Thanks
Javier Cia

Posts: 10
Joined: 02 January 2006