?‍? ?‍? Examples for teachers - Algorithms

Sub Hanoi (n As Int, SrcPeg As Peg, DestPeg As Peg, TempPeg As Peg) As ResumableSub
    If n > 0 Then
        Wait For (Hanoi(n - 1, SrcPeg, TempPeg, DestPeg)) Complete (unused As Boolean)
        Wait For (MoveDisk(SrcPeg, DestPeg)) Complete (unused As Boolean)
        Wait For (Hanoi(n - 1, TempPeg, DestPeg, SrcPeg)) Complete (unused As Boolean)
    End If
    Return True
End Sub

'Non-UI application (console / server application)
Sub AppStart (Args() As String)
    Log(SplitMultiply("1234", "0002", 4))
    Log(SplitMultiply("80001", "12341", 5))
End Sub

Sub SplitMultiply (x As String, y As String, n As Int) As String
    If n = 1 Then
        Return GetDigitFromString(x, 0) * GetDigitFromString(y, 0) 'one digit * one digit
    Else
        Dim m As Int = Ceil(n / 2)
        Dim a As String = DivideBy10M(x, m)
        Dim b As String = Modulo10M(x, m)
        Dim c As String = DivideBy10M(y, m)
        Dim d As String = Modulo10M(y, m)
        Dim e As String = SplitMultiply(a, c, m)
        Dim f As String = SplitMultiply(b, d, m)
        Dim g As String = SplitMultiply(b, c, m)
        Dim h As String = SplitMultiply(a, d, m)
    End If
    'the strings will be parsed here and later converted back to a string.
    'we use NumberFormat2 to control the formatting.
    Return NumberFormat2(ShiftByM(e, 2 * m) + ShiftByM(g + h, m) + f, 0, 0, 0, False)
End Sub

Sub GetDigitFromString(s As String, index As Int) As Int
    Return "" & s.CharAt(index)
End Sub

Sub DivideBy10M (s As String, m As Int) As String
    If s.Length <= m Then Return "0"
    Return s.SubString2(0, s.Length - m)
End Sub

Sub Modulo10M (s As String, m As Int) As String
    Return s.SubString(s.Length - m)
End Sub

Sub ShiftByM(s As String, m As Int) As String
    For i = 0 To m - 1
        s = s & "0"
    Next
    Return s
End Sub

'Non-UI application (console / server application)
Sub AppStart (Args() As String)
    Dim x As List
    x.Initialize
    x.AddAll(Array As Int(8, 6, 7, 5, 3, 10, 9)) 'we cannot use x = Array(..) as it will create a read-only list.
    Dim Target As Int = 33
    If ConstructSubset(x, Target) Then
        Dim sb As StringBuilder
        sb.Initialize
        For Each v As Int In x
            If sb.Length > 0 Then sb.Append(" + ")
            sb.Append(v)
        Next
        sb.Append(" = ").Append(Target)
        Log(sb.ToString)
    Else
        Log("No solution")
    End If
End Sub

'Finds a single subset that add up to Target.
'Modifies the input list.
Sub ConstructSubset (X As List, Target As Int) As Boolean
    If Target = 0 Then
        'remove all remaining values
        X.Clear
        Return True
    End If
    If Target < 0 Or X.Size = 0 Then
        Return False
    End If
    Dim CurrentValue As Int = X.Get(0)
    X.RemoveAt(0)
    'without current value
    Dim res As Boolean = ConstructSubset(X, Target)
    If res Then Return True
     'with current value
    res = ConstructSubset(X, Target - CurrentValue)
    'put the value back in the list
    X.InsertAt(0, CurrentValue)
    Return res
End Sub