September 2017 Update

Task/Digital-root/Kotlin/digital-root.kotlin

@@ -0,0 +1,36 @@
+// version 1.0.6
+
+fun sumDigits(n: Long): Int = when {
+        n < 0L -> throw IllegalArgumentException("Negative numbers not allowed")
+        else   -> {
+            var sum = 0
+            var nn  = n
+            while (nn > 0L) {
+                sum += (nn % 10).toInt()
+                nn /= 10
+            }
+            sum
+        }
+    }
+
+fun digitalRoot(n: Long): Pair<Int, Int> = when {
+        n < 0L  -> throw IllegalArgumentException("Negative numbers not allowed")
+        n < 10L -> Pair(n.toInt(), 0)
+        else    -> {
+            var dr = n
+            var ap = 0
+            while (dr > 9L) {
+                dr = sumDigits(dr).toLong()
+                ap++
+            }
+            Pair(dr.toInt(), ap)
+        }
+    }
+
+fun main(args: Array<String>) {
+    val a = longArrayOf(1, 14, 267, 8128, 627615, 39390, 588225, 393900588225)
+    for (n in a) {
+        val(dr, ap) = digitalRoot(n)
+        println("${n.toString().padEnd(12)} has additive persistence $ap and digital root of $dr")
+    }
+}