I know that this post contain some kind of a stupid question. But, as I read and understand that, an empty Sudoku grid is also considered to be a valid Sudoku grid (provided that to exclude minimum 17 clues and unique solution constraint).

Also, I am not interested in speed for a moment (but considered added information, if one supplied). However, interested to know about steps taken to find first solution only.

Here I am sharing my solver empty Sudoku grid solution step wise, which only search through Naked/Hidden Singles/Tuples, Box-Line/Pointing and Claiming Intersection Removals, Basic Fish (i.e., X-Wing, Sword Fish and Jelly Fish) and Trial-and-Error strategies. I am not interested/planning to implement rating in my Solver near future.

My Bitwise Sudoku Solver program solves empty Sudoku grid, without backtracking, as follows:

- Code: Select all
`0) Apply Trial and Error Candidate 1 from Candidates 123456789 at Cell 0`

1) Apply Trial and Error Candidate 2 from Candidates 23456789 at Cell 1

2) Apply Trial and Error Candidate 3 from Candidates 3456789 at Cell 2

3) Apply Trial and Error Candidate 4 from Candidates 456789 at Cell 3

4) Apply Trial and Error Candidate 5 from Candidates 56789 at Cell 4

5) Apply Trial and Error Candidate 6 from Candidates 6789 at Cell 5

36) Found Naked triplet Candidates 789 at Unit 20 Cells 6 7 8

6) Apply Trial and Error Candidate 7 from Candidates 789 at Cell 6

7) Apply Trial and Error Candidate 8 from Candidates 89 at Cell 7

8) Apply Naked Single Candidate 9 from Candidates 9 at Cell 8

9) Apply Trial and Error Candidate 4 from Candidates 456789 at Cell 9

10) Apply Trial and Error Candidate 5 from Candidates 56789 at Cell 10

11) Apply Trial and Error Candidate 6 from Candidates 6789 at Cell 11

100) Found Hidden triplet Candidates 789 at Unit 1 Cells 12 13 14

36) Found Naked triplet Candidates 789 at Unit 2 Cells 18 19 20

100) Found Naked triplet Candidates 123 at Unit 2 Cells 21 22 23

12) Apply Trial and Error Candidate 7 from Candidates 789 at Cell 12

13) Apply Trial and Error Candidate 8 from Candidates 89 at Cell 13

14) Apply Naked Single Candidate 9 from Candidates 9 at Cell 14

15) Apply Trial and Error Candidate 1 from Candidates 123 at Cell 15

16) Apply Trial and Error Candidate 2 from Candidates 23 at Cell 16

17) Apply Naked Single Candidate 3 from Candidates 3 at Cell 17

18) Apply Trial and Error Candidate 7 from Candidates 789 at Cell 18

19) Apply Trial and Error Candidate 8 from Candidates 89 at Cell 19

20) Apply Naked Single Candidate 9 from Candidates 9 at Cell 20

21) Apply Trial and Error Candidate 1 from Candidates 123 at Cell 21

22) Apply Trial and Error Candidate 2 from Candidates 23 at Cell 22

23) Apply Naked Single Candidate 3 from Candidates 3 at Cell 23

24) Apply Trial and Error Candidate 4 from Candidates 456 at Cell 24

25) Apply Trial and Error Candidate 5 from Candidates 56 at Cell 25

26) Apply Naked Single Candidate 6 from Candidates 6 at Cell 26

27) Apply Trial and Error Candidate 2 from Candidates 235689 at Cell 27

28) Apply Trial and Error Candidate 1 from Candidates 14578 at Cell 29

29) Apply Trial and Error Candidate 4 from Candidates 4578 at Cell 32

30) Apply Trial and Error Candidate 5 from Candidates 578 at Cell 35

31) Apply Trial and Error Candidate 3 from Candidates 3679 at Cell 31

32) Apply Trial and Error Candidate 6 from Candidates 679 at Cell 28

33) Apply Hidden Single Candidate 7 from Candidates 79 at Cell 34

34) Apply Trial and Error Candidate 8 from Candidates 89 at Cell 33

35) Apply Naked Single Candidate 9 from Candidates 9 at Cell 30

36) Apply Trial and Error Candidate 1 from Candidates 167 at Cell 40

37) Apply Trial and Error Candidate 2 from Candidates 24 at Cell 44

38) Apply Trial and Error Candidate 6 from Candidates 67 at Cell 49

77) Found Naked triplet Candidates 479 at Unit 25 Cells 58 67 76

39) Apply Trial and Error Candidate 5 from Candidates 58 at Cell 39

40) Apply Trial and Error Candidate 7 from Candidates 78 at Cell 41

22) Found Naked pair Candidates 28 at Unit 5 Cells 48 50

41) Apply Trial and Error Candidate 2 from Candidates 28 at Cell 48

42) Apply Naked Single Candidate 8 from Candidates 8 at Cell 50

43) Apply Trial and Error Candidate 4 from Candidates 48 at Cell 38

44) Apply Hidden Single Candidate 8 from Candidates 389 at Cell 36

35) Found Hidden pair Candidates 14 at Unit 5 Cells 52 53

45) Apply Trial and Error Candidate 5 from Candidates 57 at Cell 47

46) Apply Hidden Single Candidate 7 from Candidates 379 at Cell 46

47) Apply Trial and Error Candidate 3 from Candidates 39 at Cell 45

48) Apply Naked Single Candidate 9 from Candidates 9 at Cell 37

49) Apply Naked Single Candidate 9 from Candidates 9 at Cell 51

50) Apply Trial and Error Candidate 3 from Candidates 36 at Cell 42

51) Apply Naked Single Candidate 6 from Candidates 6 at Cell 43

52) Apply Trial and Error Candidate 1 from Candidates 14 at Cell 52

53) Apply Naked Single Candidate 4 from Candidates 4 at Cell 53

54) Apply Trial and Error Candidate 5 from Candidates 569 at Cell 54

55) Apply Trial and Error Candidate 1 from Candidates 12 at Cell 59

56) Apply Trial and Error Candidate 3 from Candidates 34 at Cell 55

28) Found Hidden pair Candidates 49 at Unit 6 Cells 58 61

57) Apply Trial and Error Candidate 6 from Candidates 68 at Cell 57

58) Apply Naked Single Candidate 2 from Candidates 2 at Cell 60

59) Apply Trial and Error Candidate 7 from Candidates 78 at Cell 56

60) Apply Naked Single Candidate 8 from Candidates 8 at Cell 62

61) Apply Trial and Error Candidate 4 from Candidates 49 at Cell 61

62) Apply Naked Single Candidate 9 from Candidates 9 at Cell 58

63) Apply Trial and Error Candidate 6 from Candidates 69 at Cell 63

64) Apply Naked Single Candidate 5 from Candidates 5 at Cell 69

65) Apply Naked Single Candidate 2 from Candidates 2 at Cell 68

66) Apply Naked Single Candidate 8 from Candidates 8 at Cell 65

67) Apply Naked Single Candidate 3 from Candidates 3 at Cell 66

68) Apply Naked Single Candidate 9 from Candidates 9 at Cell 70

69) Apply Naked Single Candidate 9 from Candidates 9 at Cell 72

70) Apply Naked Single Candidate 2 from Candidates 2 at Cell 74

71) Apply Naked Single Candidate 8 from Candidates 8 at Cell 75

72) Apply Naked Single Candidate 5 from Candidates 5 at Cell 77

73) Apply Naked Single Candidate 6 from Candidates 6 at Cell 78

74) Apply Naked Single Candidate 3 from Candidates 3 at Cell 79

75) Apply Trial and Error Candidate 1 from Candidates 17 at Cell 71

76) Apply Naked Single Candidate 4 from Candidates 4 at Cell 64

77) Apply Hidden Single Candidate 4 from Candidates 47 at Cell 76

78) Apply Naked Single Candidate 1 from Candidates 1 at Cell 73

79) Apply Naked Single Candidate 7 from Candidates 7 at Cell 67

80) Apply Naked Single Candidate 7 from Candidates 7 at Cell 80

1) 123456789456789123789123456261934875894517362375268914537691248648372591912845637 # S1 # N0 # H4 # 15.000000

It takes following steps:

- Code: Select all
`1. Naked Single = 30`

2. Hidden Single = 04

3. Trial and Error = 47

4. Naked pair = 01

5. Hidden pair = 02

6. Naked triplet = 04

7. Hidden triplet = 01

====

Total steps = 89

R. Jamil

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Place the word "only" anywhere on the sentence:

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