added assignment 4 ex 3 with pattern matching

src/Assignment4/Ex3_ListsMatch.sc

@@ -0,0 +1,79 @@
+import scala.annotation.tailrec
+
+
+// Complexity: O(n)
+@tailrec
+def last[T](list: List[T]): T = {
+  list.tail match {
+    case Nil => list.head
+    case _ => last(list.tail)
+  }
+}
+
+def init[T](list: List[T]): List[T] = {
+  list.tail match {
+    case Nil => Nil
+    case _ => list.head::init(list.tail)
+  }
+}
+
+// Complexity: O(n)
+def concat[T](l1: List[T], l2: List[T]): List[T] = {
+  l1 match {
+    case Nil => l2
+    case _ => l1.head::concat(l1.tail, l2)
+  }
+}
+
+// Complexity: O(n²)
+def reverse[T](list: List[T]): List[T] = {
+  list match {
+    case Nil => Nil
+    case _ => last(list)::reverse(init(list))
+  }
+}
+
+// Better -> O(n)
+/*
+def reverse[T](list: List[T], res: List[T] = Nil): List[T] = {
+  list match {
+    case Nil => res
+    case _ => reverse(list.tail, list.head::res)
+  }
+}
+*/
+
+def take[T](list: List[T], n: Int): List[T] = {
+  if (n <= 0) Nil
+  else list match {
+    case Nil => Nil
+    case _ => list.head::take(list.tail, n - 1)
+  }
+}
+
+@tailrec
+def drop[T](list: List[T], n: Int): List[T] = {
+  if (n <= 0) list
+  else list match {
+    case Nil => list
+    case _ => drop(list.tail, n - 1)
+  }
+}
+
+@tailrec
+def apply[T](list: List[T], n: Int): T = {
+  n match {
+    case 0 => list.head
+    case _ => apply(list.tail, n - 1)
+  }
+}
+
+
+assert(last(List(1,2,3)) == 3)
+assert(init(List(1,2,3)) == List(1,2))
+assert(concat(List(1,2,3), List(4,5,6)) == List(1,2,3,4,5,6))
+assert(reverse(List(1,2,3)) == List(3,2,1))
+assert(take(List(1,2,3), 2) == List(1,2))
+assert(drop(List(1,2,3), 2) == List(3))
+assert(drop(List(1,2,3), 4) == Nil)
+assert(apply(List(1,2,3), 2) == 3)