implement prefix average in recursive way

src/main/kotlin/it/norangeb/algorithms/exercises/PrefixAverage.kt

@@ -6,7 +6,7 @@
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * to use, copy, modify, tryMerge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
@@ -25,19 +25,29 @@
 
 package it.norangeb.algorithms.exercises
 
-class PrefixAverage {
-    companion object {
-        fun prefixAverage(arrayIn: IntArray): IntArray {
+object PrefixAverage {
+    fun prefixAverage(arrayIn: IntArray): IntArray {
 
-            val arrayOut = IntArray(arrayIn.size)
-            var currentSum = 0
+        val arrayOut = IntArray(arrayIn.size)
+        var currentSum = 0
 
-            for (i in 0 until arrayIn.size) {
-                currentSum += arrayIn[i]
-                arrayOut[i] = currentSum / (i + 1)
+        for (i in 0 until arrayIn.size) {
+            currentSum += arrayIn[i]
+            arrayOut[i] = currentSum / (i + 1)
+        }
+
+        return arrayOut
+    }
+
+    fun recursivePrefixAverage(arrayIn: IntArray, position: Int = 0, acc: Int = 0): IntArray {
+        return when (position) {
+            arrayIn.size -> IntArray(arrayIn.size)
+            else -> {
+                val newAcc = arrayIn[position] + acc
+                val array = recursivePrefixAverage(arrayIn, position + 1, newAcc)
+                array[position] = newAcc / (position + 1)
+                array
             }
-
-            return arrayOut
         }
     }
 }

src/test/kotlin/it/norangeb/algorithms/exercises/PrefixAverageTest.kt

@@ -67,4 +67,42 @@ class PrefixAverageTest {
 
         arrayOut `should equal` intArrayOf(21, 21, 21, 21, 21)
     }
+
+    @Test
+    fun testNominalCaseRecursive() {
+        val arrayIn = intArrayOf(21, 23, 25, 31, 20, 18, 16)
+
+        val arrayOut = PrefixAverage.recursivePrefixAverage(arrayIn)
+
+        arrayOut `should equal` intArrayOf(
+            21, 22, 23, 25, 24, 23, 22
+        )
+    }
+
+    @Test
+    fun testEmptyArrayRecursive() {
+        val arrayIn = intArrayOf()
+
+        val arrayOut = PrefixAverage.recursivePrefixAverage(arrayIn)
+
+        arrayOut `should equal` intArrayOf()
+    }
+
+    @Test
+    fun testOneElementArrayRecursive() {
+        val arrayIn = intArrayOf(25)
+
+        val arrayOut = PrefixAverage.recursivePrefixAverage(arrayIn)
+
+        arrayOut `should equal` intArrayOf(25)
+    }
+
+    @Test
+    fun testAlwaysSameElementArrayRecursive() {
+        val arrayIn = intArrayOf(21, 21, 21, 21, 21)
+
+        val arrayOut = PrefixAverage.recursivePrefixAverage(arrayIn)
+
+        arrayOut `should equal` intArrayOf(21, 21, 21, 21, 21)
+    }
 }