From 31c7ce3b7119a1e42c95021a8b784bfdd02908b3 Mon Sep 17 00:00:00 2001
From: thebinarysoul <willymyfriend@gmail.com>
Date: Sat, 25 Jun 2022 15:52:50 +0300
Subject: [PATCH] Quick Sort List

---
 DIRECTORY.md                                |  2 +
 src/main/scala/Sort/QuickSortList.scala     | 41 +++++++++++++++++++++
 src/test/scala/Sort/QuickSortListSpec.scala | 20 ++++++++++
 3 files changed, 63 insertions(+)
 create mode 100644 src/main/scala/Sort/QuickSortList.scala
 create mode 100644 src/test/scala/Sort/QuickSortListSpec.scala

diff --git a/DIRECTORY.md b/DIRECTORY.md
index b48aa26..ac87a1e 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -29,6 +29,7 @@
         * [Quicksort](https://github.com/TheAlgorithms/Scala/blob/master/src/main/scala/Sort/QuickSort.scala)
         * [Recursiveinsertionsort](https://github.com/TheAlgorithms/Scala/blob/master/src/main/scala/Sort/RecursiveInsertionSort.scala)
         * [Selectionsort](https://github.com/TheAlgorithms/Scala/blob/master/src/main/scala/Sort/SelectionSort.scala)
+        * [Quicksortlist](https://github.com/TheAlgorithms/Scala/blob/master/src/main/scala/Sort/QuickSortList.scala)
   * Test
       * Dynamicprogramming
         * [Coinchangespec](https://github.com/TheAlgorithms/Scala/blob/master/src/test/scala/DynamicProgramming/CoinChangeSpec.scala)
@@ -56,3 +57,4 @@
         * [Quicksortspec](https://github.com/TheAlgorithms/Scala/blob/master/src/test/scala/Sort/QuickSortSpec.scala)
         * [Recursiveinsertionsortspec](https://github.com/TheAlgorithms/Scala/blob/master/src/test/scala/Sort/RecursiveInsertionSortSpec.scala)
         * [Selectionsortspec](https://github.com/TheAlgorithms/Scala/blob/master/src/test/scala/Sort/SelectionSortSpec.scala)
+        * [Quicksortlistspec](https://github.com/TheAlgorithms/Scala/blob/master/src/test/scala/Sort/QuickSortListSpec.scala)
diff --git a/src/main/scala/Sort/QuickSortList.scala b/src/main/scala/Sort/QuickSortList.scala
new file mode 100644
index 0000000..612eebc
--- /dev/null
+++ b/src/main/scala/Sort/QuickSortList.scala
@@ -0,0 +1,41 @@
+package Sort
+
+import scala.annotation.tailrec
+
+/** An implementation of quicksort algorithm to sort of an unsorted integer list
+  */
+object QuickSortList {
+  /** @param list
+    *   - a List of unsorted integers
+    * @return
+    *   - a list of sorted integers
+    */
+  def quickSortList(list: List[Int]): List[Int] = list match {
+    case Nil => list
+    case pivot :: other =>
+      sort(pivot, other, Nil, Nil) match {
+        case (left, right) => quickSortList(left) ::: pivot :: quickSortList(right)
+      }
+  }
+
+  /** @param piv
+    *   - a pivot element
+    * @param rem
+    *   - remaining elements of the list
+    * @param left
+    *   - a list of integers less than piv
+    * @param right
+    *   - a list of integers great than piv
+    * @return
+    *   (l, r)
+    */
+  @tailrec
+  private def sort(piv: Int, rem: List[Int], left: List[Int], right: List[Int]): (List[Int], List[Int]) = {
+    rem match {
+      case head :: tail =>
+        if (piv > head) sort(piv, tail, head :: left, right)
+        else sort(piv, tail, left, head :: right)
+      case Nil => (left, right)
+    }
+  }
+}
diff --git a/src/test/scala/Sort/QuickSortListSpec.scala b/src/test/scala/Sort/QuickSortListSpec.scala
new file mode 100644
index 0000000..71dfe60
--- /dev/null
+++ b/src/test/scala/Sort/QuickSortListSpec.scala
@@ -0,0 +1,20 @@
+package Sort
+
+import org.scalatest.flatspec.AnyFlatSpec
+
+class QuickSortListSpec extends AnyFlatSpec {
+  "A Quick Sort List" should "return a sorted version of a list passed to it" in {
+    val list = List(3, 2, 7, 1, 9, 0)
+    assert(QuickSortList.quickSortList(list) === List(0, 1, 2, 3, 7, 9))
+  }
+
+  "A Quick Sort List" should "return empty list when empty list is passed to it" in {
+    val list = List.empty[Int]
+    assert(QuickSortList.quickSortList(list) === Nil)
+  }
+
+  "A Quick Sort List" should "not modify list" in {
+    val list = List(0, 1, 2, 3, 7, 9)
+    assert(QuickSortList.quickSortList(list) === List(0, 1, 2, 3, 7, 9))
+  }
+}