Assignment_05/src/main/scala/Main.scala

   1
   2 object Main {
   3   // Question 1: HOF on lists.
   4   def lengthStrings(l: List[String]) = l map (_ length)
   5   def dup[T](e: T, n: Int) = (1 to n) map (_ => e)
   6   def dot(l1: List[Int], l2: List[Int]) = (l1 zip l2) map { case (a, b) => a * b }
   7
   8   // Question 2: Folding functions on lists.
   9   def areTrue(l: List[Boolean]) = l reduceLeft (_ && _)
  10   def lString(l: List[String]): Int = l.foldLeft(0)((acc, s) => acc + s.length())
  11   def longest(l: List[String]): (Int, String) = l.foldLeft(0, ""){ case (curr@(len, longestStr), str) => if (str.length() > len) (str.length(), str) else curr }
  12   def isPresent[T](l: List[T], e: T): Boolean = l.foldLeft(false)((acc, e2) => acc || e == e2)
  13   def flattenList[T](l: List[T]): List[T] = l.foldRight (List.empty[T]) ((e: T, acc: List[T]) =>
  14     e match {
  15       case l: List[T] => flattenList(l) ++ acc
  16       case _ => e :: acc
  17     }
  18   )
  19
  20   def main(args: Array[String]): Unit = {
  21     println("Question 1")
  22     println(s"a) ${lengthStrings(List("How", "long", "are", "we?"))}")
  23     println(s"b) ${dup("foo", 5)}")
  24     println(s"c) ${dot(List(1, 2, 3), List(2, 4, 3))}")
  25
  26     println("Question 2")
  27     println("a)")
  28     println(s"${areTrue(List(true, true, false))}")
  29     println(s"${areTrue(List(true, true, true))}")
  30     println("b)")
  31     println(s"${lString(List("Folding", "is", "fun"))}")
  32     println("c)")
  33     println(s"${longest(List("What", "is", "the", "longest?"))}")
  34     println("d)")
  35     println(s"${isPresent(List(1, 2, 3, 4), 5)}")
  36     println(s"${isPresent(List(1, 2, 3, 4), 3)}")
  37     println("e)")
  38     val l = List(List(1, 1), 2, List(3, List(5, 8)));
  39     println(s"flattenList($l): ${flattenList(l)}")
  40   }
  41 }