Imports System
Imports System.Collections.Generic
Public Class Program
Public Shared Sub PrintSubstringWithKDistinctChars(ByVal s As String, ByVal k As Integer)
Dim list As IList(Of String) = New List(Of String)()
For i As Integer = 0 To s.Length - 1
Dim ch As Char = s(i)
Dim tmp As String = "" & ch
Dim _set As ISet(Of Char) = New HashSet(Of Char)()
_set.Add(ch)
For j As Integer = i + 1 To s.Length - 1
Dim next_ch As Char = s(j)
_set.Add(next_ch)
tmp += next_ch
If tmp.Length >= k AndAlso _set.Count = k Then
list.Add(tmp)
End If
Next
Next
Console.WriteLine(String.Join(", ", list))
End Sub
Public Shared Sub Main(ByVal args As String())
Dim str As String = "characters"
Dim k As Integer = 4
PrintSubstringWithKDistinctChars(str, k)
End Sub
End Class
' run:
'
' char, chara, charac, harac, aract, ract, acte, cter, ters
'
'
