Initial data commit

Task/Move-to-front-algorithm/Scala/move-to-front-algorithm.scala

@@ -0,0 +1,97 @@
+package rosetta
+
+import scala.annotation.tailrec
+
+object MoveToFront {
+  /**
+   *  Default radix
+   */
+  private val R = 256
+
+  /**
+   *  Default symbol table
+   */
+  private def symbolTable = (0 until R).map(_.toChar).mkString
+
+  /**
+   *  Apply move-to-front encoding using default symbol table.
+   */
+  def encode(s: String): List[Int] = {
+    encode(s, symbolTable)
+  }
+
+  /**
+   *  Apply move-to-front encoding using symbol table <tt>symTable</tt>.
+   */
+  def encode(s: String, symTable: String): List[Int] = {
+    val table = symTable.toCharArray
+
+    @inline @tailrec def moveToFront(ch: Char, index: Int, tmpout: Char): Int = {
+      val tmpin = table(index)
+      table(index) = tmpout
+      if (ch != tmpin)
+        moveToFront(ch, index + 1, tmpin)
+      else {
+        table(0) = ch
+        index
+      }
+    }
+
+    @tailrec def encodeString(output: List[Int], s: List[Char]): List[Int] = s match {
+      case Nil => output
+      case x :: xs => {
+        encodeString(moveToFront(x, 0, table(0)) :: output, s.tail)
+      }
+    }
+    encodeString(Nil, s.toList).reverse
+  }
+
+  /**
+   *  Apply move-to-front decoding using default symbol table.
+   */
+  def decode(ints: List[Int]): String = {
+    decode(ints, symbolTable)
+  }
+
+  /**
+   *  Apply move-to-front decoding using symbol table <tt>symTable</tt>.
+   */
+  def decode(lst: List[Int], symTable: String): String = {
+    val table = symTable.toCharArray
+
+    @inline def moveToFront(c: Char, index: Int) {
+      for (i <- index-1 to 0 by -1)
+        table(i+1) = table(i)
+      table(0) = c
+    }
+
+    @tailrec def decodeList(output: List[Char], lst: List[Int]): List[Char] = lst match {
+      case Nil => output
+      case x :: xs => {
+        val c = table(x)
+        moveToFront(c, x)
+        decodeList(c :: output, xs)
+      }
+    }
+    decodeList(Nil, lst).reverse.mkString
+  }
+
+  def test(toEncode: String, symTable: String) {
+		val encoded = encode(toEncode, symTable)
+		println(toEncode + ": " + encoded)
+		val decoded = decode(encoded, symTable)
+		if (toEncode != decoded)
+		  print("in")
+		println("correctly decoded to " + decoded)
+	}
+}
+
+/**
+ * Unit tests the <tt>MoveToFront</tt> data type.
+ */
+object RosettaCodeMTF extends App {
+	val symTable = "abcdefghijklmnopqrstuvwxyz"
+	MoveToFront.test("broood", symTable)
+	MoveToFront.test("bananaaa", symTable)
+	MoveToFront.test("hiphophiphop", symTable)
+}