added midterm preparation

src/MidTermPrep1/Ex1.sc

@@ -0,0 +1,29 @@
+import scala.annotation.tailrec
+
+def foo(x: Int): Int = {
+  println("Foo !")
+  x + 1
+}
+
+def bar(x: => Int): Unit = {
+  println("x1=" + x)
+  println("x2=" + x)
+}
+
+bar(foo(3))
+// Foo !
+// x1=4
+// Foo !
+// x2=4
+
+
+def toUpper(s: String): String = {
+  @tailrec
+  def helper(s: String, res: String): String = {
+    if (s.isEmpty) res
+    else helper(s.tail, res + s.head.toUpper)
+  }
+  helper(s, "")
+}
+
+toUpper("hello")

src/MidTermPrep1/Ex2.sc

@@ -0,0 +1,20 @@
+import scala.annotation.tailrec
+
+def balanceMatch(chars: List[Char]): Boolean = {
+  @tailrec
+  def checkStep(chars: List[Char], n: Int): Boolean = {
+    if (chars.isEmpty) n == 0
+    else if (n < 0) false
+    else checkStep(chars.tail, chars.head match {
+      case '(' => n + 1
+      case ')' => n - 1
+      case _ => n
+    })
+  }
+  checkStep(chars, 0)
+}
+
+balanceMatch("(if (x == 0) then max (1, x))".toList)
+balanceMatch("I told him (that it's not (yet) done). (But he wasn't listening)".toList)
+balanceMatch(")".toList)
+balanceMatch("())()".toList)

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")