added midterm preparation

src/MidTermPrep1/Ex3.sc

@@ -0,0 +1,36 @@
+import scala.annotation.tailrec
+
+def countTrue(bools: List[Boolean]): Int = {
+  bools.foldLeft(0)((n, bool) => if (bool) n + 1 else n)
+}
+
+countTrue(List(true, true, false, true, false, false))
+
+def remDup[T](list: List[T]): List[T] = {
+  list.foldRight(List.empty[T])((elem: T, res: List[T]) => {
+    if (res.contains(elem)) res
+    else elem::res
+  })
+}
+
+def remDup2[T](list: List[T]): List[T] = {
+  list.foldLeft(List.empty[T])((res: List[T], elem: T) => {
+    if (res.contains(elem)) res
+    else res :+ elem
+  })
+}
+
+def remDup3[T](list: List[T]): List[T] = {
+  @tailrec
+  def helper(list: List[T], distinct: List[T]): List[T] = {
+    list match {
+      case head::rest if distinct.contains(head) => helper(rest, distinct)
+      case head::rest => helper(rest, distinct :+ head)
+      case Nil => distinct
+    }
+  }
+  helper(list, List.empty[T])
+}
+
+remDup(List(5,3,2,4,3,2,3,3)) // List(5,3,2,4)
+remDup(List("hello", "youpi", "hello", "hello")) // List("hello", "youpi")