Data commit

Task/LZW-compression/Java/lzw-compression-1.java

@@ -0,0 +1,67 @@
+import java.util.*;
+
+public class LZW {
+    /** Compress a string to a list of output symbols. */
+    public static List<Integer> compress(String uncompressed) {
+        // Build the dictionary.
+        int dictSize = 256;
+        Map<String,Integer> dictionary = new HashMap<String,Integer>();
+        for (int i = 0; i < 256; i++)
+            dictionary.put("" + (char)i, i);
+
+        String w = "";
+        List<Integer> result = new ArrayList<Integer>();
+        for (char c : uncompressed.toCharArray()) {
+            String wc = w + c;
+            if (dictionary.containsKey(wc))
+                w = wc;
+            else {
+                result.add(dictionary.get(w));
+                // Add wc to the dictionary.
+                dictionary.put(wc, dictSize++);
+                w = "" + c;
+            }
+        }
+
+        // Output the code for w.
+        if (!w.equals(""))
+            result.add(dictionary.get(w));
+        return result;
+    }
+
+    /** Decompress a list of output ks to a string. */
+    public static String decompress(List<Integer> compressed) {
+        // Build the dictionary.
+        int dictSize = 256;
+        Map<Integer,String> dictionary = new HashMap<Integer,String>();
+        for (int i = 0; i < 256; i++)
+            dictionary.put(i, "" + (char)i);
+
+        String w = "" + (char)(int)compressed.remove(0);
+        StringBuffer result = new StringBuffer(w);
+        for (int k : compressed) {
+            String entry;
+            if (dictionary.containsKey(k))
+                entry = dictionary.get(k);
+            else if (k == dictSize)
+                entry = w + w.charAt(0);
+            else
+                throw new IllegalArgumentException("Bad compressed k: " + k);
+
+            result.append(entry);
+
+            // Add w+entry[0] to the dictionary.
+            dictionary.put(dictSize++, w + entry.charAt(0));
+
+            w = entry;
+        }
+        return result.toString();
+    }
+
+    public static void main(String[] args) {
+        List<Integer> compressed = compress("TOBEORNOTTOBEORTOBEORNOT");
+        System.out.println(compressed);
+        String decompressed = decompress(compressed);
+        System.out.println(decompressed);
+    }
+}

Task/LZW-compression/Java/lzw-compression-2.java

@@ -0,0 +1,2 @@
+[84, 79, 66, 69, 79, 82, 78, 79, 84, 256, 258, 260, 265, 259, 261, 263]
+TOBEORNOTTOBEORTOBEORNOT