Dim Shared As Integer cuadricula(9, 9), cuadriculaResuelta(9, 9)

Function isSafe(i As Integer, j As Integer, n As Integer) As Boolean
    Dim As Integer iMin, jMin, f, c

    If cuadricula(i, j) <> 0 Then Return (cuadricula(i, j) = n)

    'cuadricula(i, j) es una celda vacía. Compruebe si n está OK
    'primero revisa la fila i
    For f = 1 To 9
        If cuadricula(i, f) = n Then Return False
    Next f

    'ahora comprueba la columna j
    For c = 1 To 9
        If cuadricula(c, j) = n Then Return False
    Next c

    'finalmente, compruebe el subcuadrado de 3x3 que contiene cuadricula(i,j)
    iMin = 1 + 3 * Int((i - 1) / 3)
    jMin = 1 + 3 * Int((j - 1) / 3)
    For c = iMin To iMin + 2
        For f = jMin To jMin + 2
            If cuadricula(c, f) = n Then Return False
        Next f
    Next c

    'todas las pruebas estuvieron OK
    Return True
End Function

Sub Resolver(i As Integer, j As Integer)
    Dim As Integer f, c, n, temp
    If i > 9 Then
        'salir con cuadriculaResuelta = cuadricula
        For c = 1 To 9
            For f = 1 To 9
                cuadriculaResuelta(c, f) = cuadricula(c, f)
            Next f
        Next c
        Exit Sub
    End If
    For n = 1 To 9
        If isSafe(i, j, n) Then
            temp = cuadricula(i, j)
            cuadricula(i, j) = n
            If j = 9 Then
                Resolver i + 1, 1
            Else
                Resolver i, j + 1
            End If
            cuadricula(i, j) = temp
        End If
    Next n
End Sub

Dim As String s(9)
'inicializar la cuadrícula usando 9 cadenas, una por fila
s(1) = "001005070"
s(2) = "920600000"
s(3) = "008000600"
s(4) = "090020401"
s(5) = "000000000"
s(6) = "304080090"
s(7) = "007000300"
s(8) = "000007069"
s(9) = "010800700"

Dim As Integer i, j
For i = 1 To 9
    For j = 1 To 9
        cuadricula(i, j) = Int(Val(Mid(s(i), j, 1)))
    Next j
Next i

Resolver 1, 1
Print "Solucion:"
Color 12: Print "---------+---------+---------"
For i = 1 To 9
    For j = 1 To 9
        Color 7: Print cuadriculaResuelta(i, j); " ";
        Color 12
        If (j Mod 3 = 0) And (j <> 9) Then Color 12: Print "|";
    Next j
    If (i Mod 3 = 0) Then Print !"\n---------+---------+---------" Else Print
Next i
Sleep