null handling for middle of linked list exercise

Author: andersonkmi

src/main/scala/org/codecraftlabs/leetcode/MiddleLinkedList.scala

@@ -1,12 +1,15 @@
 package org.codecraftlabs.leetcode
 
 object MiddleLinkedList {
-  def middleNode(head: ListNode): ListNode = {
-    if(head == null) null
+  def middleNode(head: ListNode): Option[ListNode] = {
+    val rootNode = Option(head)
 
-    val size = length(head)
-    val middle = size / 2
-    elementAt(middle, head)
+    rootNode match {
+      case None => None
+      case _ => val size = length(head)
+                val middle = size / 2
+                Option(elementAt(middle, head))
+    }
   }
 
   private def length(root: ListNode): Int = {

src/test/scala/org/codecraftlabs/leetcode/MiddleLinkedListSpec.scala

@@ -4,15 +4,15 @@ import org.codecraftlabs.leetcode.MiddleLinkedList.middleNode
 import org.scalatest.{FlatSpec, Matchers}
 
 class MiddleLinkedListSpec extends FlatSpec with Matchers {
-  "Null list" should "return null" in {
-    middleNode(null) shouldBe null
+  "Null list" should "return None" in {
+    middleNode(null) shouldBe None
   }
 
   "Single node list" should "return first node" in {
     val item = new ListNode(1)
     val result = middleNode(item)
-    result should not be null
-    result.x shouldEqual 1
+    result should not be None
+    result.get.x shouldEqual 1
   }
 
   "Even sized list" should "return first element of second half of the list" in {
@@ -21,8 +21,8 @@ class MiddleLinkedListSpec extends FlatSpec with Matchers {
     firstNode.next = secondNode
 
     val result = middleNode(firstNode)
-    result should not be null
-    result.x should equal(1)
+    result should not be None
+    result.get.x should equal(1)
   }
 
   "Odd size list" should "return exactly the middle element" in {
@@ -34,7 +34,7 @@ class MiddleLinkedListSpec extends FlatSpec with Matchers {
     secondNode.next = thirdNode
 
     val result = middleNode(firstNode)
-    result should not be null
-    result.x should equal(1)
+    result should not be None
+    result.get.x should equal(1)
   }
 }