Sync

Task/LZW-compression/Objeck/lzw-compression.objeck

@@ -0,0 +1,104 @@
+use Collection;
+
+class LZW {
+  function : Main(args : String[]) ~ Nil {
+    compressed := Compress("TOBEORNOTTOBEORTOBEORNOT");
+    Show(compressed);
+    decompressed := Decompress(compressed);
+    decompressed->PrintLine();
+  }
+
+  function : native : Compress(uncompressed : String) ~ IntVector {
+    # Build the dictionary.
+    dictSize := 256;
+      dictionary := StringMap->New();
+      for (i := 0; i < 256; i+=1;) {
+        key := "";
+        key->Append(i->As(Char));
+        dictionary->Insert(key, IntHolder->New(i));
+    };
+
+    w := "";
+    result := IntVector->New();
+
+    each (i : uncompressed) {
+      c := uncompressed->Get(i);
+      wc := String->New(w);
+      wc->Append(c);
+        if (dictionary->Has(wc)) {
+          w := wc;
+        }
+        else {
+          value := dictionary->Find(w)->As(IntHolder);
+          result->AddBack(value->Get());
+          # Add wc to the dictionary.
+          dictionary->Insert(wc, IntHolder->New(dictSize));
+          dictSize+=1;
+          w := "";
+          w->Append(c);
+        };
+      };
+
+      # Output the code for w.
+      if (w->Size() > 0) {
+        value := dictionary->Find(w)->As(IntHolder);
+        result->AddBack(value->Get());
+      };
+
+      return result;
+  }
+
+  function : Decompress(compressed : IntVector) ~ String {
+    # Build the dictionary.
+    dictSize := 256;
+    dictionary := IntMap->New();
+    for (i := 0; i < 256; i+=1;) {
+      value := "";
+      value->Append(i->As(Char));
+      dictionary->Insert(i, value);
+    };
+
+    w := "";
+    found := compressed->Remove(0);
+    w->Append(found->As(Char));
+
+    result := String->New(w);
+    each (i : compressed) {
+      k := compressed->Get(i);
+
+      entry : String;
+      if (dictionary->Has(k)) {
+        entry := dictionary->Find(k);
+      }
+      else if (k = dictSize) {
+        entry := String->New(w);
+        entry->Append(w->Get(0));
+      }
+      else {
+        return "";
+      };
+      result->Append(entry);
+
+      # Add w+entry[0] to the dictionary.
+      value := String->New(w);
+      value->Append(entry->Get(0));
+      dictionary->Insert(dictSize, value);
+      dictSize+=1;
+
+      w := entry;
+    };
+
+    return result;
+  }
+
+  function : Show(results : IntVector) ~ Nil {
+    "["->Print();
+    each(i : results) {
+      results->Get(i)->Print();
+      if(i + 1 < results->Size()) {
+        ", "->Print();
+      };
+    };
+    "]"->PrintLine();
+  }
+}

Task/LZW-compression/Scala/lzw-compression.scala

@@ -0,0 +1,18 @@
+ // for now, only compress
+def compress(tc:String) = {
+    //initial dictionary
+    val startDict = (1 to 255).map(a=>(""+a.toChar,a)).toMap
+    val (fullDict, result, remain) = tc.foldLeft ((startDict, List[Int](), "")) {
+      case ((dict,res,leftOver),nextChar) =>
+        if (dict.contains(leftOver + nextChar)) // current substring already in dict
+          (dict, res, leftOver+nextChar)
+        else if (dict.size < 4096) // add to dictionary
+          (dict + ((leftOver+nextChar, dict.size+1)), dict(leftOver) :: res, ""+nextChar)
+        else // dictionary is full
+          (dict, dict(leftOver) :: res, ""+nextChar)
+    }
+    if (remain.isEmpty) result.reverse else (fullDict(remain) :: result).reverse
+}
+
+// test
+compress("TOBEORNOTTOBEORTOBEORNOT")