Sudoku Puzzle Generator

Sudoku puzzles can be generated by a switching the rows and columns of a valid puzzle.
The switch has to be done between the 123, 456 and 789 rows/columns. ie; 1 cannot be switched with 7 for example.

A random pair can be generated and if a loop is run say 50 times, we get a new puzzle.
Then the cells can be hidden again randomly.

The following code generates the puzzle from a base character string which is converted to a 81 length Char array.

The output is the solution as well as the puzzle with blank (or 0s)

        


     Dim stdArray As String = "317849265245736891869512473456398712732164958981257634174925386693481527528673149"
        Dim charArray() As Char = stdArray.ToCharArray
        Dim rng As New Random
        Dim m As Integer
        Dim row1 As Integer
        Dim row2 As Integer
        Dim col1 As Integer
        Dim col2 As Integer


        Dim i As Integer
        Dim cell1 As Integer
        Dim cell2 As Integer
        Dim tempC As Char
        Dim k As Integer

        For k = 1 To 50
            m = rng.Next(1, 4)
            row1 = rng.Next(1, 4)
            row2 = rng.Next(1, 4)
            If row2 = row1 Then row2 = rng.Next(1, 4)
            If row2 = row1 Then row2 = rng.Next(1, 4)
            If row2 = row1 Then row2 = rng.Next(1, 4)
            row1 = row1 + ((m - 1) * 3)
            row2 = row2 + ((m - 1) * 3)

            m = rng.Next(1, 4)
            col1 = rng.Next(1, 4)
            col2 = rng.Next(1, 4)
            If col2 = col1 Then col2 = rng.Next(1, 4)
            If col2 = col1 Then col2 = rng.Next(1, 4)
            If col2 = col1 Then col2 = rng.Next(1, 4)
            col1 = col1 + ((m - 1) * 3)
            col2 = col2 + ((m - 1) * 3)

            For i = 1 To 9
                cell1 = ((row1 - 1) * 9) + i
                cell2 = ((row2 - 1) * 9) + i
                tempC = charArray(cell1 - 1)
                charArray(cell1 - 1) = charArray(cell2 - 1)
                charArray(cell2 - 1) = tempC
            Next
            For i = 1 To 9
                cell1 = ((i - 1) * 9) + col1
                cell2 = ((i - 1) * 9) + col2
                tempC = charArray(cell1 - 1)
                charArray(cell1 - 1) = charArray(cell2 - 1)
                charArray(cell2 - 1) = tempC
            Next
        Next


        Dim px0(80) As Char
        Dim pxb(80) As Char
        For k = 0 To 80
            px0(k) = charArray(k)
            pxb(k) = charArray(k)
        Next

        For k = 1 To 52
            m = rng.Next(0, 81)
            px0(m) = "0"
            pxb(m) = " "

        Next