## stuck on a tough one from sudoku for dummies

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

### stuck on a tough one from sudoku for dummies

I can't seem to see what clue I am missing to get the next number.

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

- 4 7 | 2 - 8 | 3 - -
8 - - | 7 - 5 | 4 - 2
- - 2 | 9 - 4 | 8 1 7

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

Thank you for any help!
wbharris

Posts: 2
Joined: 14 January 2006

could you please show the givens then i might be able to help
Chessmaster

Posts: 191
Joined: 21 December 2005

these are the given numbers:

7 - 3 | 8 - - |- - 4
- - - | - 5 7 | - - -
- - - | - - - | 2 - 8

- 4 - | 2 - 8 | 3 - -
8 - - | 7 - 5 | - - 2
- - 2 | 9 - 4 | - 1 -

2 - 9 | - - - | - - -
- - - | 4 7 - | - - -
6 - - | - - 9 | 1 - 3

Thank you again for the help!
wbharris

Posts: 2
Joined: 14 January 2006

Pappocom sumarily rejects this puzzle so it will require advanced techniques to solve. It seems that Suboku for dummies isn't for dummies after all. I'll guarantee you someone on this forum can solve it though (unless it has multiple answers).
Hud

Posts: 570
Joined: 29 October 2005

wbharris wrote:these are the given numbers:

7 - 3 | 8 - - |- - 4
- - - | - 5 7 | - - -
- - - | - - - | 2 - 8

- 4 - | 2 - 8 | 3 - -
8 - - | 7 - 5 | - - 2
- - 2 | 9 - 4 | - 1 -

2 - 9 | - - - | - - -
- - - | 4 7 - | - - -
6 - - | - - 9 | 1 - 3

Thank you again for the help!

According to Sadmans Sudoku Software this puzzle is rated hard and has one solution.

No special techniques are used to solve it though

Marc
md68

Posts: 3
Joined: 14 January 2006

Hud wrote:Pappocom sumarily rejects this puzzle so it will require advanced techniques to solve. It seems that Suboku for dummies isn't for dummies after all. I'll guarantee you someone on this forum can solve it though (unless it has multiple answers).

Pappocom rejects *lots* of puzzles, some of which are demonstrably trivial. This puzzle, though requiring a single somewhat advanced tactic, is NOT a difficult puzzle. Even if there were no community to share tactics, most bright enthusiasts would figure out this type of deduction, assuming they use pencilmarks.

Pencil marks will be needed for most people to finish this puzzle.

Code: Select all
` 7 1 3 | 8 9 2 | . . 4  4 2 8 | 6 5 7 | 9 3 1  . . . | . 4 . | 2 7 8 -------+-------+------ . 4 7 | 2 . 8 | 3 . .  8 . . | 7 . 5 | 4 . 2  . . 2 | 9 . 4 | 8 1 7 -------+-------+------ 2 . 9 | . 8 . | 7 4 .  . 8 . | 4 7 . | . 2 9  6 7 4 | 5 2 9 | 1 8 3 `

Code: Select all
`  7    1    3    | 8    9    2    | 56   56   4      4    2    8    | 6    5    7    | 9    3    1      59   569  56   | 13   4    13   | 2    7    8     ----------------+----------------+----------------  1x59 4    7    | 2    16   8    | 3   +569 +56     8    369  16   | 7    136  5    | 4    69   2      35   356  2    | 9    36   4    | 8    1    7     ----------------+----------------+----------------  2    35   9    | 13   8    136  | 7    4    56     135  8    15   | 4    7    136  | 56   2    9      6    7    4    | 5    2    9    | 1    8    3    `

The only places for a 5 in box 6 are the two cells (marked with +) r4c89. This excludes the 5 from r4c1 (marked with x)

Code: Select all
`  7    1     3   | 8    9    2    | 56   56   4      4    2     8   | 6    5    7    | 9    3    1      59   569   56  | 13   4    13   | 2    7    8     ----------------+----------------+---------------- +19   4     7   | 2    16   8    | 3    569  56     8    36x9  +16 | 7    136  5    | 4   +69   2      35   356   2   | 9    36   4    | 8    1    7     ----------------+----------------+----------------  2    35    9   | 13   8    136  | 7    4    56     135  8     15  | 4    7    136  | 56   2    9      6    7     4   | 5    2    9    | 1    8    3    `

Now there is an xy-wing:
r5c8=9 => r5c2<>9
r5c8=6 => r5c3=1 => r4c1=9 => r5c2<>9
Therefore, r5c2<>9.

After this, the rest of the puzzle can be solved with single elimination, starting with r4c1=9.

Code: Select all
`  7    1    3    | 8    9    2    | 56   56   4      4    2    8    | 6    5    7    | 9    3    1      59   569  56   |+13   4   +13   | 2    7    8     ----------------+----------------+----------------  159  4    7    | 2    16   8    | 3    569  56     8    369  16   | 7    136  5    | 4    69   2      35   356  2    | 9    36   4    | 8    1    7     ----------------+----------------+----------------  2    35   9    |+13   8    x136 | 7    4    56     135  8    15   | 4    7    136  | 56   2    9      6    7    4    | 5    2    9    | 1    8    3    `

Above is an even better solution:

r37c46 form a UNIQUE RECTANGLE. If r7c6 were [13], the puzzle would have two solutions. This is not allowed, therefore, r7c6 MUST BE 6. (Remember, unique rectangles must be in TWO rows, TWO columns and TWO boxes or they don't work.)

After this placement, the rest is trivial.
tso

Posts: 798
Joined: 22 June 2005

### Re: stuck on a tough one from sudoku for dummies

wbharris wrote:I can't seem to see what clue I am missing to get the next number.

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

- 4 7 | 2 - 8 | 3 - -
8 - - | 7 - 5 | 4 - 2
- - 2 | 9 - 4 | 8 1 7

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

Thank you for any help!

So far that is what i get for solving step...maybe some you already have made...

Block 6: row 4 must contain 5, removing 5 from candidates for r4c1
Block 7: row 8 must contain 1, removing 1 from candidates for r8c6
r5c8 = 9: forced from either candidate of r5c3 (r5c3=1 => r8c3=5 => r8c7=6 => r1c7=5 => r1c8=6 => r5c8=9), (r5c3=6 => r5c8=9)
r4c1 = 9: only cell in row 4 that can contain 9
r8c9 = 9: only cell in row 8 that can contain 9
Block 6: row 4 must contain 5, removing 5 from candidates for r4c1
Block 7: row 8 must contain 1, removing 1 from candidates for r8c6
r5c8 = 9: forced from either candidate of r5c3 (r5c3=1 => r8c3=5 => r8c7=6 => r1c7=5 => r1c8=6 => r5c8=9), (r5c3=6 => r5c8=9)
r4c1 = 9: only cell in row 4 that can contain 9
r3c1 = 5: only possible value for this cell
md68

Posts: 3
Joined: 14 January 2006

I guess I just can't count on Pappocom's ratings for my uses. Occasionally, Pappocom rates them as very hard, then says trial and error or other techniques are required.
I just don't understand why a puzzle will be rejected if simple techniques only are required. It sounds like the program is flawed.
I no longer fool with puzzles that Pappocom rejects.
Hud

Posts: 570
Joined: 29 October 2005

Hud wrote:I just don't understand why a puzzle will be rejected if simple techniques only are required. It sounds like the program is flawed.

No, Pappocom's program is not flawed. The xy-wing required to solve this puzzle is not a "simple" technique, though it may be simple to you. Keep in mind that Pappocom's program hasn't been updated for some time and a number of solving techniques have been discovered/documented since its release.
angusj

Posts: 306
Joined: 12 June 2005

Angus, I've done many Pappocom puzzles that included xy wings and I don't understand why they would be rejected when dubbing in a puzzle that only requires that technique or lesser techniques to solve them.

I'm pretty much a novice when it comes to these puzzles, but these inconsistensies tend to confuse me.
Hud

Posts: 570
Joined: 29 October 2005

Hud wrote:Angus, I've done many Pappocom puzzles that included xy wings and I don't understand why they would be rejected when dubbing in a puzzle that only requires that technique or lesser techniques to solve them.

I'm pretty much a novice when it comes to these puzzles, but these inconsistensies tend to confuse me.

The solver may choose to look for -- and will probably find -- xy-wings in even the simplest puzzles. However, ALL puzzles produced by Pappocom software can be solved by methods that are generally considered less advanced -- though the relative complexity or difficulty of a tactic is certainly both subjective and dependant on the way you solve the puzzle -- whether you use pencil marks, filtering, etc. I've used forcing chains to solve Sudokus for over 20 years -- though until recently, very few published puzzles *required* forcing chains to solve. (Pappocom's Very Hard's are actually more difficult that nearly all published Nikoli.)

Wayne's puzzles are for the pencil and paper crowd, not the software helper crowd. He believes that tactics like Swordfish are just too hard for a human to find without computer assistance.

As far as inconsistancies -- in that case I've got to side with Wayne. The puzzles are not rated on the existance of one tactic or another, but by some complex system that weight various tactics required. Any rating system has to be subjective at its roots. Which is harder -- a puzzle with 4 x-wings or one with a single Swordfish? Even a 5 or 6 cell forcing chain can be obvious to anyone but a rank beginner even without access to any of the information in this forum if it appears at the tail end of the puzzle when there are only 10 cells left to fill. Another that requires only hidden pairs and locked candidates might be very tough if a long series of these are required at the top of the puzzle when the solver is forced to to enter 6 or more candidates in a large number of cells.

(On the possibility that you're confusing xy-wings with x-wings -- the latter *is* a useful tactic in harder Pappocom puzzles.)
tso

Posts: 798
Joined: 22 June 2005