dev merge sort

scala/src/main/scala/ch12_sorts/MergeSort.scala

@@ -0,0 +1,60 @@
+package ch12_sorts
+
+object MergeSort {
+
+  def mergeSort(items: Array[Int]): Array[Int] = {
+    _mergeSort(items, 0, items.length - 1)
+    items
+  }
+
+
+  private[this] def _mergeSort(items: Array[Int], p: Int, r: Int): Unit = {
+    if (p >= r) {
+      return
+    }
+
+    val q = p + (r - p) / 2
+    _mergeSort(items, p, q)
+    _mergeSort(items, q + 1, r)
+    _merge(items, p, q, r)
+
+  }
+
+  private[this] def _merge(items: Array[Int], p: Int, q: Int, r: Int): Unit = {
+    //start of first half
+    var i = p
+    //start of second half
+    var j = q + 1
+    var k = 0
+    //temp array to hold the data
+    val tempArray = new Array[Int](r - p + 1)
+    while (i <= q && j <= r) {
+      if (items(i) <= items(j)) {
+        tempArray(k) = items(i)
+        i += 1
+      } else {
+        tempArray(k) = items(j)
+        j += 1
+      }
+      k += 1
+    }
+
+    var start = i
+    var end = q
+
+    if (j <= r) {
+      start = j
+      end = r
+    }
+
+    for (n <- start to end) {
+      tempArray(k) = items(n)
+      k += 1
+    }
+
+    //copy tempArray back to items
+    for (n <- 0 to r - p) {
+      items(p + n) = tempArray(n)
+    }
+  }
+}

scala/src/test/scala/ch11_sorts/SortsTest.scala

@@ -6,7 +6,7 @@ import scala.util.Random
 
 class SortsTest extends FlatSpec with Matchers {
 
-  behavior of "SortsTest"
+  behavior of "SortsTest in ch11"
 
   it should "bubbleSort int arrays" in {
     var array = Array(4, 5, 6, 3, 2, 1)

scala/src/test/scala/ch12_sorts/MergeSortTest.scala

@@ -0,0 +1,22 @@
+package ch12_sorts
+
+
+import org.scalatest.{FlatSpec, Matchers}
+
+class MergeSortTest extends FlatSpec with Matchers {
+  behavior of "SortsTest in ch12"
+
+  it should "mergeSort int arrays" in {
+    var array = Array(4, 5, 6, 3, 2, 1)
+    array = MergeSort.mergeSort(array)
+    array.mkString("") should equal("123456")
+
+    array = Array(4)
+    array = MergeSort.mergeSort(array)
+    array.mkString("") should equal("4")
+
+    array = Array(4, 2)
+    array = MergeSort.mergeSort(array)
+    array.mkString("") should equal("24")
+  }
+}