Merge branch 'release/v1.0.20.0'

Author: andersonkmi

README.md

@@ -33,8 +33,11 @@ to keep up with the language and learn how to use the Scala test library as well
 * Partition list
 * Add binary
 * Contains duplicate
+* Middle of linked list
 
 ## Versions
+* v1.0.20.0 (10/06/2018) - Added Middle of linked list exercise.
+
 * v1.0.19.0 (10/04/2018) - Added Contains duplicate exercise.
 
 * v1.0.18.0 (09/26/2018) - Added add binary exercise.

build.sbt

@@ -5,7 +5,7 @@ lazy val root = (project in file(".")).
     inThisBuild(List(
       organization := "org.codecraftlabs",
       scalaVersion := "2.12.7",
-      version      := "1.0.19.0"
+      version      := "1.0.20.0"
     )),
     name := "leetcode-scala",
     libraryDependencies += scalaTest % Test,

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

@@ -0,0 +1,32 @@
+package org.codecraftlabs.leetcode
+
+object MiddleLinkedList {
+  def middleNode(head: ListNode): ListNode = {
+    if(head == null) null
+
+    val size = length(head)
+    val middle = size / 2
+    elementAt(middle, head)
+  }
+
+  private def length(root: ListNode): Int = {
+    count(root)
+  }
+
+  private def count(node: ListNode): Int = {
+    if(node != null) {
+      1 + count(node.next)
+    } else 0
+  }
+
+  private def elementAt(position: Int, node: ListNode): ListNode = {
+    var counter = 0
+    var item = node
+    while (counter < position) {
+      item = item.next
+      counter += 1
+    }
+    item
+  }
+
+}

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

@@ -0,0 +1,40 @@
+package org.codecraftlabs.leetcode
+
+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
+  }
+
+  "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
+  }
+
+  "Even sized list" should "return first element of second half of the list" in {
+    val firstNode = new ListNode(0)
+    val secondNode = new ListNode(1)
+    firstNode.next = secondNode
+
+    val result = middleNode(firstNode)
+    result should not be null
+    result.x should equal(1)
+  }
+
+  "Odd size list" should "return exactly the middle element" in {
+    val firstNode = new ListNode(0)
+    val secondNode = new ListNode(1)
+    val thirdNode = new ListNode(2)
+
+    firstNode.next = secondNode
+    secondNode.next = thirdNode
+
+    val result = middleNode(firstNode)
+    result should not be null
+    result.x should equal(1)
+  }
+}