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Beginner’s Guide to Code Algorithms

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STEP 3

Check all rows.

For k =​ 1 To 9

  If i <> k Then

    ‘ For m =​ 1 To 9

    If sbox(k, j) > 0 Then

      foundincantbelist =​ 0

      For kk =​ 1 To 9

        If sbox(k, j) =​ cantbelist(i, j, kk) Then foundincantbelist =​ 1

      Next kk

        If foundincantbelist =​ 0 Then

          cantbelist(i, j, NextEmptyLocation(i, j)) =​ sbox(k, j)

        End If

        End If

      ‘ Next m

    End If

  Next k:

:

Next i

STEP 4

Now we need to examine each cell in the 3 by 3 matrix this cell belongs to. The

algorithm used to find the row and column values for the 3 by 3 grid is very simple.

Both for row and column, the technique is to find the closest multiple of 3 and then

add 1, 2, and 3 to it. The “int” function helps with this by removing the decimals.

For example, the multiple of 3 closest to 7 is 6. You can get that by running this

formula:

Int((i -​ 1) /​ 3) * 3 where i is 7.

  For k =​ 1 To 3

    n =​ Int((i -​ 1) /​ 3) * 3 +​ k

    For l =​ 1 To 3

      p =​ Int((j -​ 1) /​ 3) * 3 +​ l

      If (l =​ n And j =​ p) Then

        m =​ m ‘(do nothing)

      Else

        If sbox(n, p) <> ““ Then

          foundincantbelist =​ 0

          For kk =​ 1 To 9

          If sbox(n, p) =​ cantbelist(i, j, kk) Then foundincantbelist =​ 1

          Next kk

          If foundincantbelist =​ 0 Then

          cantbelist(i, j, NextEmptyLocation(i, j)) =​ sbox(n, p)

          End If

        End If

        End If

    Next l

  Next k

Now that the “cantbelist” is built, we can simply check its contents. Any empty

cell with eight values (from 1 to 9) in “cantbelist” must be assigned the ninth digit.

This next code does exactly that.