new files

Task/Ackermann-function/Scala/ackermann-function-3.scala

@@ -0,0 +1,40 @@
+val maxDepth = 4
+
+val ackMMap  = scala.collection.mutable.Map[BigInt, BigInt]()
+val ackNMaps = Array.fill(maxDepth + 1) { scala.collection.mutable.Map[BigInt, BigInt]() }
+
+def ack(m: Int, n: BigInt): BigInt = {
+    if ((m < 0) || (n < 0)) {
+        throw new Exception("Negative parameters are not allowed: ack(%s, %s)".format(m, n))
+    }
+    if (m > maxDepth) {
+        throw new Exception("First parameter is greater as %s: ack(%s, %s)".format(maxDepth, m, n))
+    }
+
+    val newM        = m - 1
+    val newN        = n - 1
+
+    if (m == 0) {
+        n + 1
+    } else if (n == 0) {
+        ackMMap.getOrElseUpdate(newM, ack(newM, 1))
+    } else {
+        val createStep   = 125
+        val index        = m
+        val mapCurrent   = ackNMaps(index)
+        val mapPrevious  = ackNMaps(index - 1)
+        val maxRecursion = 2 * createStep
+        val nrOfElements : BigInt = if (mapCurrent.isEmpty) 0 else mapCurrent.max._1
+
+        if ((nrOfElements + maxRecursion) < n) {
+            for (i <- nrOfElements + createStep to n by createStep) {
+                mapCurrent.getOrElseUpdate(i, ack(m, i))
+            }
+        }
+        mapCurrent.getOrElseUpdate(n, {
+            val ackVal = mapCurrent.getOrElseUpdate(newN, ack(m, newN))
+
+            mapPrevious.getOrElseUpdate(ackVal, ack(newM, ackVal))
+        })
+    }
+}