Imports System
Imports System.Collections.Generic
Imports System.Text.RegularExpressions
Module LongestSharedPrefix
' Extract alphabetic words (lowercased)
Function ExtractWords(text As String) As List(Of String)
Dim words As New List(Of String)()
Dim m = Regex.Matches(text, "[A-Za-z]+")
For Each match As Match In m
words.Add(match.Value.ToLower())
Next
Return words
End Function
' Build prefix → list of words that share that prefix
Function GroupByPrefixes(words As List(Of String)) As Dictionary(Of String, List(Of String))
Dim groups As New Dictionary(Of String, List(Of String))()
For Each w In words
For i = 1 To w.Length
Dim prefix = w.Substring(0, i)
If Not groups.ContainsKey(prefix) Then
groups(prefix) = New List(Of String)()
End If
groups(prefix).Add(w)
Next
Next
Return groups
End Function
' Find the longest prefix that appears in 2+ words
Function LongestSharedPrefix(groups As Dictionary(Of String, List(Of String))) As String
Dim best As String = ""
For Each kvp In groups
Dim prefix = kvp.Key
Dim list = kvp.Value
If list.Count >= 2 AndAlso prefix.Length > best.Length Then
best = prefix
End If
Next
Return best
End Function
Sub Main()
Dim text As String =
"The Lowly inhabitants of the lowland were surprised to see " &
"the lower branches of the trees."
Dim words = ExtractWords(text)
Dim groups = GroupByPrefixes(words)
Dim prefix = LongestSharedPrefix(groups)
If prefix <> "" Then
Dim group = groups(prefix)
Console.WriteLine("Longest shared prefix:")
Console.WriteLine($"{prefix} | prefix_len={prefix.Length} | group_count={group.Count} | [{String.Join(", ", group)}]")
Else
Console.WriteLine("No shared prefix found.")
End If
End Sub
End Module
' run:
'
' Longest shared prefix:
' lowl | prefix_len=4 | group_count=2 | [lowly, lowland]
'
