September 2017 Update

Task/Move-to-front-algorithm/Kotlin/move-to-front-algorithm.kotlin

@@ -0,0 +1,48 @@
+// version 1.1.2
+
+fun encode(s: String): IntArray {
+    if (s.isEmpty()) return intArrayOf()
+    val symbols = "abcdefghijklmnopqrstuvwxyz".toCharArray()
+    val result = IntArray(s.length)
+    for ((i, c) in s.withIndex()) {
+        val index = symbols.indexOf(c)
+        if (index == -1)
+            throw IllegalArgumentException("$s contains a non-alphabetic character")
+        result[i] = index
+        if (index == 0) continue
+        for (j in index - 1 downTo 0) symbols[j + 1] = symbols[j]
+        symbols[0] = c
+    }
+    return result
+}
+
+fun decode(a: IntArray): String {
+    if (a.isEmpty()) return ""
+    val symbols = "abcdefghijklmnopqrstuvwxyz".toCharArray()
+    val result = CharArray(a.size)
+    for ((i, n) in a.withIndex()) {
+        if (n !in 0..25)
+            throw IllegalArgumentException("${a.contentToString()} contains an invalid number")
+        result[i] = symbols[n]
+        if (n == 0) continue
+        for (j in n - 1 downTo 0) symbols[j + 1] = symbols[j]
+        symbols[0] = result[i]
+    }
+    return result.joinToString("")
+}
+
+fun main(args: Array<String>) {
+    val strings = arrayOf("broood", "bananaaa", "hiphophiphop")
+    val encoded = Array<IntArray?>(strings.size) { null }
+    for ((i, s) in strings.withIndex()) {
+        encoded[i] = encode(s)
+        println("${s.padEnd(12)} -> ${encoded[i]!!.contentToString()}")
+    }
+    println()
+    val decoded = Array<String?>(encoded.size) { null }
+    for ((i, a) in encoded.withIndex()) {
+        decoded[i] = decode(a!!)
+        print("${a.contentToString().padEnd(38)} -> ${decoded[i]!!.padEnd(12)}")
+        println(" -> ${if (decoded[i] == strings[i]) "correct" else "incorrect"}")
+    }
+}