September 2017 Update

Task/LZW-compression/REALbasic/lzw-compression.realbasic

@@ -0,0 +1,105 @@
+    Function compress(str as String) As String
+      Dim i as integer
+      Dim w as String = ""
+      Dim c as String
+      Dim strLen as Integer
+      Dim wc as string
+      Dim dic() as string
+      Dim result() as string
+      Dim lookup as integer
+      Dim startPos as integer = 0
+      Dim combined as String
+
+      strLen = len(str)
+
+      dic = populateDictionary
+
+      for i = 1 to strLen
+        c = str.mid(i, 1)
+        wc = w + c
+
+        startPos = getStartPos(wc)
+
+        lookup = findArrayPos(dic, wc, startPos)
+        if (lookup <> -1) then
+          w = wc
+        Else
+          startPos = getStartPos(w)
+          lookup = findArrayPos(dic, w, startPos)
+          if lookup <> -1 then
+            result.Append(lookup.ToText)
+          end if
+          dic.append(wc)
+          w = c
+        end if
+      next i
+
+      if (w <> "") then
+        startPos = getStartPos(w)
+        lookup = findArrayPos(dic, w, startPos)
+        result.Append(lookup.ToText)
+      end if
+
+      return join(result, ",")
+    End Function
+
+    Function decompress(str as string) As string
+      dim comStr() as string
+      dim w as string
+      dim result as string
+      dim comStrLen as integer
+      dim entry as string
+      dim dic() as string
+      dim i as integer
+
+      comStr = str.Split(",")
+      comStrLen = comStr.Ubound
+      dic = populateDictionary
+
+      w = chr(val(comStr(0)))
+      result = w
+      for i = 1 to comStrLen
+        entry = dic(val(comStr(i)))
+        result = result + entry
+        dic.append(w + entry.mid(1,1))
+        w = entry
+      next i
+
+      return result
+    End Function
+
+    Private Function findArrayPos(arr() as String, search as String, start as integer) As Integer
+      dim arraySize as Integer
+      dim arrayPosition as Integer = -1
+      dim i as Integer
+
+      arraySize = UBound(arr)
+
+      for i = start to arraySize
+        if (strcomp(arr(i), search, 0) = 0) then
+          arrayPosition = i
+          exit
+        end if
+      next i
+
+      return arrayPosition
+    End Function
+
+    Private Function getStartPos(str as String) As integer
+      if (len(str) = 1) then
+        return 0
+      else
+        return 255
+      end if
+    End Function
+
+    Private Function populateDictionary() As string()
+      dim dic() as string
+      dim i as integer
+
+      for i = 0 to 255
+        dic.append(Chr(i))
+      next i
+
+      return dic
+    End Function