'Visual Basic 2010 Recursie Procedures en Functies
Module Example1
    Sub Main()
        Console.WriteLine(GetFaculty(0))
        Console.WriteLine(GetFaculty(1))
        Console.WriteLine(GetFaculty(2))
        Console.WriteLine(GetFaculty(3))
        Console.WriteLine(GetFaculty(4))
        Console.WriteLine(GetFaculty(5))
        '
        Console.ReadLine()
    End Sub
    Function GetFaculty(ByVal value As Integer) As Integer
        GetFaculty = 1
        For factor As Integer = value To 2 Step -1
            GetFaculty *= factor
        Next
    End Function
End Module
Module Example2
    Sub Main()
        Console.WriteLine(GetFaculty(0))
        Console.WriteLine(GetFaculty(1))
        Console.WriteLine(GetFaculty(2))
        Console.WriteLine(GetFaculty(3))
        Console.WriteLine(GetFaculty(4))
        Console.WriteLine(GetFaculty(5))
        '
        Console.ReadLine()
    End Sub
    Function GetFaculty(ByVal value As Integer) As Integer
        If value = 0 Then
            GetFaculty = 1
        Else
            GetFaculty = value * GetFaculty(value - 1)
        End If
    End Function
End Module
Module Example3
    Sub Main()
        Console.WriteLine(GetCommonDivisor(3, 9))
        Console.WriteLine(GetCommonDivisor(3, -9))
        Console.WriteLine(GetCommonDivisor(8, 3))
        Console.WriteLine(GetCommonDivisor(-3, -8))                        ' (1)
        Console.WriteLine(GetCommonDivisor(6, 0))
        Console.WriteLine(GetCommonDivisor(0, 6))
        Console.WriteLine(GetCommonDivisor(8, 12))
        Console.WriteLine(GetCommonDivisor(9, 9))
        '
        Console.ReadLine()
    End Sub
    Function GetCommonDivisor(ByVal value1 As Integer, _
                              ByVal value2 As Integer) As Integer
        If value1 < 0 Then
            GetCommonDivisor = GetCommonDivisor( value1, value2)
        ElseIf value2 < 0 Then
            GetCommonDivisor = GetCommonDivisor(value1,  value2)
        ElseIf value1 < value2 Then
            GetCommonDivisor = GetCommonDivisor(value2, value1)
        ElseIf value2 = 0 Then
            GetCommonDivisor = value1
        Else
            GetCommonDivisor = GetCommonDivisor(value2, value1 Mod value2)
        End If
    End Function
End Module
Module Example4
    Sub Main()
        Console.WriteLine(GetPower(2, 3))
        Console.WriteLine(GetPower(2, 2))
        Console.WriteLine(GetPower(2, 1))
        Console.WriteLine(GetPower(2, 0))
        Console.WriteLine(GetPower(2, -1))
        Console.WriteLine(GetPower(2, -2))
        Console.WriteLine(GetPower(2, -3))
        '
        Console.ReadLine()
    End Sub
    '
    Function GetPower(ByVal base As Integer, _
                      ByVal exponent As Integer) As Integer
        If exponent = 0 Then
            GetPower = 1
        ElseIf exponent > 0 Then
            GetPower = base * GetPower(base, exponent - 1)
        ElseIf exponent < 0 Then
            GetPower = 1 / GetPower(base, -exponent)
        End If
    End Function
End Module
Module Example5
    Sub Main()
        Console.WriteLine(GetFibo(1))
        Console.WriteLine(GetFibo(2))
        Console.WriteLine(GetFibo(3))
        Console.WriteLine(GetFibo(4))
        Console.WriteLine(GetFibo(5))
        Console.WriteLine(GetFibo(6))
        Console.WriteLine(GetFibo(7))
        Console.WriteLine(GetFibo(8))
        Console.WriteLine(GetFibo(9))
        Console.WriteLine(GetFibo(10))
        '
        Console.ReadLine()
    End Sub
    Function GetFibo(ByVal ordinal As Integer) As Integer
        If ordinal = 1 OrElse ordinal = 2 Then
            GetFibo = 1
        ElseIf ordinal > 2 Then
            GetFibo = GetFibo(ordinal - 1) + GetFibo(ordinal - 2)
        End If
    End Function
End Module
Module Example6
    Sub Main()
        Console.WriteLine(GetFibo(1))
        Console.WriteLine(GetFibo(2))
        Console.WriteLine(GetFibo(3))
        Console.WriteLine(GetFibo(4))
        Console.WriteLine(GetFibo(5))
        Console.WriteLine(GetFibo(6))
        Console.WriteLine(GetFibo(7))
        Console.WriteLine(GetFibo(8))
        Console.WriteLine(GetFibo(9))
        Console.WriteLine(GetFibo(10))
        '
        Console.ReadLine()
    End Sub
    Function GetFibo(ByVal ordinal As Byte) As Integer
        GetFibo = 1
        If ordinal > 2 Then
            Dim fibo1 As Short = 1
            Dim fibo2 As Short = 1
            Dim count As Byte = 2
            Do Until count = ordinal
                Dim backup As Integer = fibo2
                fibo2 += fibo1
                fibo1 = backup
                count += 1
            Loop
            GetFibo = fibo2
        End If
    End Function
End Module
Module QuickSort
    Sub Main()
        Dim numbers As Integer() = {88, 75, 93, 81, 21, 74, 84, 35}
        PrintArray(numbers)
        '
        QuickSort(numbers, 0, 7)
        PrintArray(numbers)
        '
        Console.ReadLine()
    End Sub
    Sub PrintArray(ByVal values As Integer())
        For Each value As Integer In values
            Console.Write(value & " ")
        Next
        Console.WriteLine()
    End Sub
    Sub QuickSort(ByVal array As Integer(), _
                  ByVal lowerbound As Integer, ByVal upperbound As Integer)
        Dim count As Integer = upperbound - lowerbound + 1
        If count = 2 Then
            If array(lowerbound) > array(upperbound) Then
                Dim backup As Integer = array(lowerbound)
                array(lowerbound) = array(upperbound)
                array(upperbound) = backup
            End If
        ElseIf count > 2 Then
            Dim pivotIndex As Integer = (lowerbound + upperbound) \ 2
            Dim pivot As Integer = array(pivotIndex)
            '
            array(pivotIndex) = array(upperbound)
            array(upperbound) = pivot
            '
            Dim smallerIndex As Integer = lowerbound
            Dim biggerIndex As Integer = upperbound
            '
            Do While smallerIndex <> biggerIndex
                '
                Do While array(smallerIndex) <= pivot AndAlso _
                         smallerIndex < biggerIndex
                    smallerIndex += 1
                Loop
                '
                Do While array(biggerIndex) >= pivot AndAlso _
                         smallerIndex < biggerIndex
                    biggerIndex -= 1
                Loop
                '
                If smallerIndex <> biggerIndex Then
                    Dim backup As Integer = array(smallerIndex)
                    array(smallerIndex) = array(biggerIndex)
                    array(biggerIndex) = backup
                End If
            Loop
            '
            array(upperbound) = array(biggerIndex)
            array(biggerIndex) = pivot
            '
            QuickSort(array, lowerbound, biggerIndex - 1)
            QuickSort(array, smallerIndex + 1, upperbound)
        End If
    End Sub
End Module
Module NQueensProblem
    ' Problem :
    ' How to assign N queens to N positions on a N by N chessboard, so that no
    ' queen can attack any other queen on the board.
    '
    ' Configuration :
    Const N As Integer = 8
    '
    Dim chessBoard(N - 1, N - 1) As Boolean
    ' elements contain True if queen is assigned to according position
    '
    Sub Main()
        If CanSolve(N) Then
            Console.WriteLine("A solution is found :")
            DrawChessBoard()
        Else
            Console.WriteLine("No solution is found.")
        End If
        '
        Console.ReadLine()
    End Sub
    Sub DrawChessBoard()
        Console.Write("+")
        For col As Integer = 0 To N - 1
            Console.Write("---+")
        Next
        Console.WriteLine()
        For row As Integer = 0 To N - 1
            Console.Write("|")
            For col As Integer = 0 To N - 1
                If HasQueen(row, col) Then
                    Console.Write(" Q |")
                Else
                    Console.Write("   |")
                End If
            Next
            Console.WriteLine()
            Console.Write("+")
            For col As Integer = 0 To N - 1
                Console.Write("---+")
            Next
            Console.WriteLine()
        Next
        Console.WriteLine()
    End Sub
    Function CanSolve(ByVal queens As Integer) As Boolean
        If queens = 0 Then
            CanSolve = True
        Else
            Dim col As Integer = N - queens
            Dim rowToTry As Integer = 0
            Do
                If IsUnderAttack(rowToTry, col) Then
                    rowToTry += 1
                Else
                    PlaceQueen(rowToTry, col)
                    Console.WriteLine("Trying :")                          ' (*)
                    DrawChessBoard()                                       ' (*)
                    CanSolve = CanSolve(queens - 1)
                    If Not CanSolve Then
                        RemoveQueen(rowToTry, col)
                        Console.WriteLine("Backtracking to :")             ' (*)
                        DrawChessBoard()                                   ' (*)
                        rowToTry += 1
                    End If
                End If
            Loop Until CanSolve OrElse Not IsLegalPosition(rowToTry, col)
        End If
        ' (*) for debugging purposes
    End Function
    Function IsUnderAttack(ByVal row As Integer, ByVal col As Integer) As Boolean
        IsUnderAttack = IsUnderAttack(row, col, -1, -1) OrElse _
                        IsUnderAttack(row, col, +1, -1) OrElse _
                        IsUnderAttack(row, col, 0, -1)
    End Function
    Function IsUnderAttack(ByVal row As Integer, ByVal col As Integer, _
                           ByVal rowOffSet As Integer, ByVal colOffSet As Integer) As Boolean
        Do
            row += rowOffSet
            col += colOffSet
        Loop While IsLegalPosition(row, col) AndAlso Not HasQueen(row, col)
        IsUnderAttack = HasQueen(row, col)
    End Function
    Function HasQueen(ByVal row As Integer, ByVal col As Integer) As Boolean
        HasQueen = IsLegalPosition(row, col) AndAlso chessBoard(row, col)
    End Function
    Function IsLegalPosition(ByVal row As Integer, ByVal col As Integer) As Boolean
        IsLegalPosition = row >= 0 AndAlso row <= N - 1 AndAlso col >= 0 AndAlso col <= N - 1
    End Function
    Sub PlaceQueen(ByVal row As Integer, ByVal col As Integer)
        chessBoard(row, col) = True
    End Sub
    Sub RemoveQueen(ByVal row As Integer, ByVal col As Integer)
        chessBoard(row, col) = False
    End Sub
End Module
Module Exercise1Task
    Sub Main()
        'Console.WriteLine(GetRowToZero(5))
        'Console.WriteLine(GetRowToZero(-3))
        'Console.WriteLine(GetRowToZero(0))
        '
        Console.ReadLine()
    End Sub
End Module
Module Exercise1Solution
    Sub Main()
        Console.WriteLine(GetRowToZero(5))
        Console.WriteLine(GetRowToZero(-3))
        Console.WriteLine(GetRowToZero(0))
        '
        Console.ReadLine()
    End Sub
    Function GetRowToZero(ByVal value As Integer) As String
        If value = 0 Then
            GetRowToZero = 0
        ElseIf value < 0 Then
            GetRowToZero = value & " " & GetRowToZero(value + 1)
        Else 'If value > 0 Then
            GetRowToZero = value & " " & GetRowToZero(value - 1)
        End If
    End Function
End Module
Module Exercise2Task
    Sub Main()
        'Console.WriteLine(GetRow(2, -3))
        'Console.WriteLine(GetRow(0, 2))
        'Console.WriteLine(GetRow(-3, -4))
        '
        Console.ReadLine()
    End Sub
End Module
Module Exercise2Solution
    Sub Main()
        Console.WriteLine(GetRow(2, -3))
        Console.WriteLine(GetRow(0, 2))
        Console.WriteLine(GetRow(-3, -4))
        '
        Console.ReadLine()
    End Sub
    Function GetRow(ByVal value1 As Integer, _
                    ByVal value2 As Integer) As String
        If value1 > value2 Then
            GetRow = GetRow(value2, value1)
        ElseIf value2 - value1 < 2 Then
            GetRow = ""
        Else
            GetRow = (value1 + 1) & " " & GetRow(value1 + 1, value2)
        End If
    End Function
End Module
Module Exercise3Task
    Sub Main()
        'PlaceSteps(2)
        Console.WriteLine()
        '
        'PlaceSteps(10)
        Console.WriteLine()
        '
        'PlaceSteps(11)
        Console.ReadLine()
    End Sub
End Module
Module Exercise3Solution
    Sub Main()
        PlaceSteps(2)
        Console.WriteLine()
        '
        PlaceSteps(10)
        Console.WriteLine()
        '
        PlaceSteps(11)
        Console.ReadLine()
    End Sub
    Sub PlaceSteps(ByVal distance As Integer)
        Dim stepDistance As Integer
        If distance = 1 Then
            stepDistance = 1
            Console.WriteLine(stepDistance)
        Else
            If distance >= 3 Then
                stepDistance = 3
            ElseIf distance >= 1 Then
                stepDistance = 1
            End If
            Console.WriteLine(stepDistance)
            PlaceSteps(distance - stepDistance)
        End If
    End Sub
End Module
Module Exercise4Task
    Sub Main()
        Dim numbers As Integer() = {1, 3, 4, 7, 9, 10, 11, 15, 18, 20}
        '
        Dim number, lowerbound, upperbound As Integer
        Dim found As Boolean
        '
        number = 15
        lowerbound = 0
        upperbound = 9
        'found = BinarySearch(number, numbers, lowerbound, upperbound)
        Console.WriteLine(found)
        '
        number = 18
        lowerbound = 0
        upperbound = 7
        'found = BinarySearch(number, numbers, lowerbound, upperbound)
        Console.WriteLine(found)
        '
        Console.ReadLine()
    End Sub
End Module
Module Exercise4Solution
    Sub Main()
        Dim numbers As Integer() = {1, 3, 4, 7, 9, 10, 11, 15, 18, 20}
        '
        Dim number, lowerbound, upperbound As Integer
        Dim found As Boolean
        '
        number = 15
        lowerbound = 0
        upperbound = 9
        found = BinarySearch(number, numbers, lowerbound, upperbound)
        Console.WriteLine(found) ' True
        '
        number = 18
        lowerbound = 0
        upperbound = 7
        found = BinarySearch(number, numbers, lowerbound, upperbound)
        Console.WriteLine(found) ' False
        '
        Console.ReadLine()
    End Sub
    Function BinarySearch(ByVal number As Integer, _
                          ByVal array As Integer(), _
                          ByVal lowerbound As Integer, _
                          ByVal upperbound As Integer) As Boolean
        Dim middle As Integer = (lowerbound + upperbound) \ 2
        If (number = array(middle)) Then
            BinarySearch = True
        Else
            If (upperbound <= lowerbound) Then
                BinarySearch = False
            Else
                If number > array(middle) Then
                    lowerbound = middle + 1
                Else
                    upperbound = middle - 1
                End If
                BinarySearch = BinarySearch(number, array, lowerbound, upperbound)
            End If
        End If
    End Function
End Module
Module Exercise5Task
    Sub Main()
        Dim diskCount As Integer = 5
        Dim source As Integer = 1
        Dim help As Integer = 2
        Dim destination As Integer = 3
        '
        'TowersOfHanoi(diskCount, source, destination, help)
        '
        Console.ReadLine()
    End Sub
End Module
Module Exercise5Solution
    Sub Main()
        Dim diskCount As Integer = 5
        Dim source As Integer = 1
        Dim help As Integer = 2
        Dim destination As Integer = 3
        '
        TowersOfHanoi(diskCount, source, destination, help)
        '
        Console.ReadLine()
    End Sub
    Sub TowersOfHanoi(ByVal diskCount As Integer, _
                      ByVal source As Integer, ByVal destination As Integer, _
                      ByVal help As Integer)
        If diskCount = 1 Then
            Console.WriteLine("from " & source & " to " & destination)
        Else
            TowersOfHanoi(diskCount - 1, source, help, destination)
            Console.WriteLine("from " & source & " to " & destination)
            TowersOfHanoi(diskCount - 1, help, destination, source)
        End If
    End Sub
End Module
Module Exercise6Task
    Sub Main()
        Dim fiboNumbers As Integer()
        'fiboNumbers = GetFiboNumbers(10)
        '
        For Each fiboNumber As Integer In fiboNumbers
            Console.Write(fiboNumber & " ")
        Next
        '
        Console.ReadLine()
    End Sub
End Module
Module Exercise6Solution
    Sub Main()
        Dim fiboNumbers As Integer()
        fiboNumbers = GetFiboNumbers(10)
        '
        For Each fiboNumber As Integer In fiboNumbers
            Console.Write(fiboNumber & " ")
        Next
        '
        Console.ReadLine()
    End Sub
    Function GetFiboNumbers(ByVal ordinal As Integer) As Integer()
        Dim fiboNumbers As Integer()
        If ordinal = 1 Then
            fiboNumbers = New Integer() {1}
        ElseIf ordinal = 2 Then
            fiboNumbers = New Integer() {1, 1}
        ElseIf ordinal > 2 Then
            fiboNumbers = GetFiboNumbers(ordinal - 1)
            ReDim Preserve fiboNumbers(ordinal - 1)
            fiboNumbers(ordinal - 1) = fiboNumbers(ordinal - 2) + _
                                       fiboNumbers(ordinal - 3)
        End If
        GetFiboNumbers = fiboNumbers
    End Function
End Module
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