Imports System
Imports System.Text
' ---------------------------------------------------------
' Compress: turn "aaabbcccc" into "a3b2c4"
' This is run-length encoding (RLE)
' ---------------------------------------------------------
Module RLE
Public Function Compress(s As String) As String
If s.Length = 0 Then Return "" ' Edge case: empty string
Dim outStr As New StringBuilder() ' Result string
Dim count As Integer = 1 ' Count of repeated characters
' Start from index 1 and compare with previous character
For i As Integer = 1 To s.Length
' If still repeating the same character, increase count
If i < s.Length AndAlso s(i) = s(i - 1) Then
count += 1
Else
' Character changed OR reached end of string
outStr.Append(s(i - 1)) ' Add the character
outStr.Append(count) ' Add how many times it repeated
count = 1 ' Reset counter
End If
Next
Return outStr.ToString()
End Function
' ---------------------------------------------------------
' Decompress: turn "a3b2c4" into "aaabbcccc"
' Reads a letter, then reads digits, expands them.
' ---------------------------------------------------------
Public Function Decompress(s As String) As String
Dim outStr As New StringBuilder() ' Result string
Dim currentChar As Char = Convert.ToChar(0) ' The character being processed
Dim number As New StringBuilder() ' Digits representing the count
For Each c As Char In s
If Char.IsLetter(c) Then ' Found a letter
' If we already have a previous letter + number, expand it
If currentChar <> Convert.ToChar(0) AndAlso number.Length > 0 Then
Dim count As Integer = Integer.Parse(number.ToString())
outStr.Append(New String(currentChar, count))
End If
currentChar = c ' Start new character
number.Clear() ' Reset number buffer
ElseIf Char.IsDigit(c) Then ' Found a digit
number.Append(c) ' Build multi-digit number
End If
Next
' Handle the last character + number pair
If currentChar <> Convert.ToChar(0) AndAlso number.Length > 0 Then
Dim count As Integer = Integer.Parse(number.ToString())
outStr.Append(New String(currentChar, count))
End If
Return outStr.ToString()
End Function
Sub Main()
Dim s As String = "wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww"
Dim c As String = Compress(s)
Dim d As String = Decompress(c)
Console.WriteLine("Original: " & s)
Console.WriteLine("Compressed: " & c)
Console.WriteLine("Decompressed: " & d)
End Sub
End Module
' run:
'
' Original: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
' Compressed: w12b1w10b3w6c4w12
' Decompressed: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
'
