September 2017 Update

Task/LZW-compression/Phix/lzw-compression.phix

@@ -0,0 +1,57 @@
+function compress(string uncompressed)
+integer dict = new_dict()
+sequence result = {}
+integer dictSize = 255, c
+string word = ""
+    for i=0 to 255 do
+        setd(""&i,i,dict)
+    end for
+    for i=1 to length(uncompressed) do
+        c = uncompressed[i]
+        if getd_index(word&c,dict) then
+            word &= c
+        else
+            result &= getd(word,dict)
+            dictSize += 1
+            setd(word&c,dictSize,dict)
+            word = ""&c
+        end if
+    end for
+    if word!="" then
+        result &= getd(word,dict)
+    end if
+    destroy_dict(dict)
+    return result
+end function
+
+function decompress(sequence compressed)
+integer dict = new_dict()
+integer dictSize = 255, k, ki
+string dent = "", result = "", word = ""
+    for i=0 to 255 do
+        setd(i,""&i,dict)
+    end for
+    for i=1 to length(compressed) do
+        k = compressed[i]
+        ki = getd_index(k,dict)
+        if ki then
+            dent = getd_by_index(ki,dict)
+        elsif k=dictSize then
+            dent = word&word[1]
+        else
+            return {NULL,i}
+        end if
+        result &= dent
+        setd(dictSize,word&dent[1],dict)
+        dictSize += 1
+        word = dent
+    end for
+    destroy_dict(dict)
+    return result
+end function
+
+constant example = "TOBEORNOTTOBEORTOBEORNOT"
+sequence com = compress(example)
+--?com
+pp(com)
+?decompress(com)