zebedee wrote:Can anyone help me pse with the Very Hard puzzle shown below.

32* | **1 | 8**

6** | 3*9 | 7**

*** | *** | 36*

------------------

5** | *13 | *2*

*38 | *7* | 5**

*6* | 59* | **3

------------------

*73 | 1** | ***

*56 | 43* | ***

**2 | 9*7 | *35

Many thanks.

Zeb

(very much a Sudoku beginner)

I hope this doesn't spoil the fun - I have to admire you guys solving these manually - getting the VBA Solver to work was hard enough.

This is a 'tricky one' so don't become depressed over it. Below is the log file of the solution.

- Code: Select all
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Iteration Number 1

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Testing for Unique Placements

Test all Digits for unique to Row/Col/Sq

Testing only Row/col in Square

Digit 2 occurs only in Column 9 - Square 3

Digit 2 not allowed Cell( 7, 9)

Digit 2 not allowed Cell( 8, 9)

Digit 4 occurs only in Column 6 - Square 5

Digit 4 not allowed Cell( 3, 6)

Digit 9 occurs only in Column 1 - Square 7

Digit 9 not allowed Cell( 3, 1)

Digit 9 not allowed Cell( 5, 1)

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Iteration Number 2

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Testing for Unique Placements

Test all Digits for unique to Row/Col/Sq

Testing only Row/col in Square

Digit 9 occurs only in Row 4 - Square 4

Digit 9 not allowed Cell( 4, 7)

Digit 9 not allowed Cell( 4, 9)

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Iteration Number 3

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Testing for Unique Placements

Test all Digits for unique to Row/Col/Sq

Testing only Row/col in Square

Testing for Pairs/Triplets [Rows]

Testing for Pairs/Triplets [Columns]

Col 7 - Digit 9 is a Pair in the same Square ~ Rows = 7, 8

Digit 9 not allowed Cell( 7, 8)

Digit 9 not allowed Cell( 8, 8)

Digit 9 not allowed Cell( 7, 9)

Digit 9 not allowed Cell( 8, 9)

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Iteration Number 4

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Testing for Unique Placements

Test all Digits for unique to Row/Col/Sq

Testing only Row/col in Square

Testing for Pairs/Triplets [Rows]

Testing for Pairs/Triplets [Columns]

Testing for x,y Pairs of Digits [Rows]

Testing for x,y Pairs of Digits [Columns]

Col 7 - Digits 2 & 9 are a Pair into Rows = 78

Digit 4 not allowed Cell( 7, 7)

Digit 6 not allowed Cell( 7, 7)

Digit 1 not allowed Cell( 8, 7)

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Iteration Number 5

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Testing for Unique Placements

Test all Digits for unique to Row/Col/Sq

Testing only Row/col in Square

Testing for Pairs/Triplets [Rows]

Testing for Pairs/Triplets [Columns]

Testing for x,y Pairs of Digits [Rows]

Testing for x,y Pairs of Digits [Columns]

Testing N-Cell Candidates [Rows]

Testing N-Cell Candidates [Cols]

Testing N-Cell Candidates [SQs]

N-Cell Rule - Candidates = 1469 in Square 6

Digit 4 not allowed Cell( 4, 9)

Digit 6 not allowed Cell( 4, 9)

Digit 1 not allowed Cell( 6, 8)

Digit 4 not allowed Cell( 6, 8)

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Iteration Number 6

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Testing for Unique Placements

Test all Digits for unique to Row/Col/Sq

Testing only Row/col in Square

Testing for Pairs/Triplets [Rows]

Testing for Pairs/Triplets [Columns]

Testing for x,y Pairs of Digits [Rows]

Testing for x,y Pairs of Digits [Columns]

Testing N-Cell Candidates [Rows]

Testing N-Cell Candidates [Cols]

Testing N-Cell Candidates [SQs]

Testing for X_Wings [Rows]

Testing for X_Wings [Columns]

X_Wing Rule - Digit 6 at Columns 6 & 9 are a Pairs into Rows = 57

Digit 6 not allowed Cell( 5, 4)

Digit 6 not allowed Cell( 7, 5)

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Iteration Number 7

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Testing for Unique Placements

35 - Digit 2 only candidate for Cell( 5, 4)

Test all Digits for unique to Row/Col/Sq

36 - Cell( 6, 1) = 2

37 - Digit 7 Only position in Column( 1) is Cell( 3, 1)

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Iteration Number 8

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Testing for Unique Placements

38 - Digit 8 only candidate for Cell( 3, 4)

39 - Digit 6 only candidate for Cell( 4, 4)

40 - Digit 4 only candidate for Cell( 4, 7)

41 - Digit 4 only candidate for Cell( 5, 6)

42 - Digit 8 only candidate for Cell( 6, 6)

43 - Digit 1 only candidate for Cell( 6, 7)

44 - Digit 7 only candidate for Cell( 6, 8)

45 - Digit 2 only candidate for Cell( 8, 6)

46 - Digit 9 only candidate for Cell( 8, 7)

47 - Digit 6 only candidate for Cell( 9, 7)

48 - Digit 7 only candidate for Cell( 1, 4)

49 - Digit 5 only candidate for Cell( 3, 6)

50 - Digit 9 only candidate for Cell( 4, 2)

51 - Digit 7 only candidate for Cell( 4, 3)

52 - Digit 8 only candidate for Cell( 4, 9)

53 - Digit 1 only candidate for Cell( 5, 1)

54 - Digit 9 only candidate for Cell( 5, 8)

55 - Digit 6 only candidate for Cell( 5, 9)

56 - Digit 4 only candidate for Cell( 6, 3)

57 - Digit 6 only candidate for Cell( 7, 6)

58 - Digit 2 only candidate for Cell( 7, 7)

59 - Digit 4 only candidate for Cell( 7, 9)

60 - Digit 8 only candidate for Cell( 8, 1)

61 - Digit 1 only candidate for Cell( 8, 8)

62 - Digit 7 only candidate for Cell( 8, 9)

All Digit = 7 allocated

63 - Digit 4 only candidate for Cell( 9, 1)

64 - Digit 1 only candidate for Cell( 9, 2)

65 - Digit 8 only candidate for Cell( 9, 5)

66 - Digit 9 only candidate for Cell( 1, 9)

67 - Digit 4 only candidate for Cell( 3, 2)

68 - Digit 2 only candidate for Cell( 3, 5)

69 - Digit 1 only candidate for Cell( 3, 9)

70 - Digit 9 only candidate for Cell( 7, 1)

71 - Digit 5 only candidate for Cell( 7, 5)

72 - Digit 8 only candidate for Cell( 7, 8)

73 - Digit 5 only candidate for Cell( 1, 3)

74 - Digit 4 only candidate for Cell( 1, 8)

75 - Digit 8 only candidate for Cell( 2, 2)

All Digit = 8 allocated

76 - Digit 1 only candidate for Cell( 2, 3)

All Digit = 1 allocated

77 - Digit 4 only candidate for Cell( 2, 5)

All Digit = 4 allocated

78 - Digit 5 only candidate for Cell( 2, 8)

All Digit = 5 allocated

79 - Digit 2 only candidate for Cell( 2, 9)

All Digit = 2 allocated

80 - Digit 9 only candidate for Cell( 3, 3)

All Digit = 9 allocated

81 - Digit 6 only candidate for Cell( 1, 5)

All Digit = 6 allocated

====================

Puzzle Solved

====================

The first 6 Iterations

are purely using rules to decide where digits cannot go

. Only then does the X-Wing rule eliminate Digit 6 at (5,4), (7,5) - and finally

the normal placement rules of each digit once in Row/Col/SQ kick in to solve the Puzzle.

The Pairs/Triplets in SQ rule is one that can be very useful, and I guess OK manually - it should be fairly obvious from above, but if (say) in a Row there only 2 (or 3) positions that a Digit can go, AND they are in the same SQ - then within the SQ we must eliminate as candidates this digit from all other cells in he SQ. Ditto if true for Columns.

As others have said - this is not easy, and those of us who enjoy the challange of writing a 'Solver' have had to work v hard to get their solvers to this level.

They can get even harder

, but once you are into swordfish rules, then you are almost out of reach by manual methods - and are into 'solver' only solutions - unless you are some kind of genius, or have somehow re-wired your brain on SuDoku patters

Good luck - don't get too hooked, it becomes an obsession