Data commit

Task/Entropy/Kotlin/entropy.kotlin

@@ -0,0 +1,33 @@
+// version 1.0.6
+
+fun log2(d: Double) = Math.log(d) / Math.log(2.0)
+
+fun shannon(s: String): Double {
+    val counters = mutableMapOf<Char, Int>()
+    for (c in s) {
+        if (counters.containsKey(c)) counters[c] = counters[c]!! + 1
+        else counters.put(c, 1)
+    }
+    val nn = s.length.toDouble()
+    var sum = 0.0
+    for (key in counters.keys) {
+       val term = counters[key]!! / nn
+       sum += term * log2(term)
+    }
+    return -sum
+}
+
+fun main(args: Array<String>) {
+    val samples = arrayOf(
+        "1223334444",
+        "1223334444555555555",
+        "122333",
+        "1227774444",
+        "aaBBcccDDDD",
+        "1234567890abcdefghijklmnopqrstuvwxyz",
+        "Rosetta Code"
+    )
+    println("            String                             Entropy")
+    println("------------------------------------      ------------------")
+    for (sample in samples) println("${sample.padEnd(36)}  ->  ${"%18.16f".format(shannon(sample))}")
+}