Data commit

Task/LZW-compression/Kotlin/lzw-compression.kotlin

@@ -0,0 +1,62 @@
+// version 1.1.2
+
+object Lzw {
+    /** Compress a string to a list of output symbols. */
+    fun compress(uncompressed: String): MutableList<Int> {
+        // Build the dictionary.
+        var dictSize = 256
+        val dictionary = mutableMapOf<String, Int>()
+        (0 until dictSize).forEach { dictionary.put(it.toChar().toString(), it)}
+
+        var w = ""
+        val result = mutableListOf<Int>()
+        for (c in uncompressed) {
+            val wc = w + c
+            if (dictionary.containsKey(wc))
+                w = wc
+            else {
+                result.add(dictionary[w]!!)
+                // Add wc to the dictionary.
+                dictionary.put(wc, dictSize++)
+                w = c.toString()
+            }
+        }
+
+        // Output the code for w
+        if (!w.isEmpty()) result.add(dictionary[w]!!)
+        return result
+    }
+
+    /** Decompress a list of output symbols to a string. */
+    fun decompress(compressed: MutableList<Int>): String {
+        // Build the dictionary.
+        var dictSize = 256
+        val dictionary = mutableMapOf<Int, String>()
+        (0 until dictSize).forEach { dictionary.put(it, it.toChar().toString())}
+
+        var w = compressed.removeAt(0).toChar().toString()
+        val result = StringBuilder(w)
+        for (k in compressed) {
+            var entry: String
+            if (dictionary.containsKey(k))
+                entry = dictionary[k]!!
+            else if (k == dictSize)
+                entry = w + w[0]
+            else
+                throw IllegalArgumentException("Bad compressed k: $k")
+            result.append(entry)
+
+            // Add w + entry[0] to the dictionary.
+            dictionary.put(dictSize++, w + entry[0])
+            w = entry
+        }
+        return result.toString()
+    }
+}
+
+fun main(args: Array<String>) {
+    val compressed = Lzw.compress("TOBEORNOTTOBEORTOBEORNOT")
+    println(compressed)
+    val decompressed = Lzw.decompress(compressed)
+    println(decompressed)
+}