Questions 1 and 2 from the fifth assignment.

[Scala.git] / Assignment_05 / src / main / scala / Main.scala

diff --git a/Assignment_05/src/main/scala/Main.scala b/Assignment_05/src/main/scala/Main.scala
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+
+object Main {
+  // Question 1: HOF on lists.
+  def lengthStrings(l: List[String]) = l map (_ length)
+  def dup[T](e: T, n: Int) = (1 to n) map (_ => e)
+  def dot(l1: List[Int], l2: List[Int]) = (l1 zip l2) map { case (a, b) => a * b }
+
+  // Question 2: Folding functions on lists.
+  def areTrue(l: List[Boolean]) = l reduceLeft (_ && _)
+  def lString(l: List[String]): Int = l.foldLeft(0)((acc, s) => acc + s.length())
+  def longest(l: List[String]): (Int, String) = l.foldLeft(0, ""){ case (curr@(len, longestStr), str) => if (str.length() > len) (str.length(), str) else curr }
+  def isPresent[T](l: List[T], e: T): Boolean = l.foldLeft(false)((acc, e2) => acc || e == e2)
+  def flattenList[T](l: List[T]): List[T] = l.foldRight (List.empty[T]) ((e: T, acc: List[T]) =>
+    e match {
+      case l: List[T] => flattenList(l) ++ acc
+      case _ => e :: acc
+    }
+  )
+
+  def main(args: Array[String]): Unit = {
+    println("Question 1")
+    println(s"a) ${lengthStrings(List("How", "long", "are", "we?"))}")
+    println(s"b) ${dup("foo", 5)}")
+    println(s"c) ${dot(List(1, 2, 3), List(2, 4, 3))}")
+
+    println("Question 2")
+    println("a)")
+    println(s"${areTrue(List(true, true, false))}")
+    println(s"${areTrue(List(true, true, true))}")
+    println("b)")
+    println(s"${lString(List("Folding", "is", "fun"))}")
+    println("c)")
+    println(s"${longest(List("What", "is", "the", "longest?"))}")
+    println("d)")
+    println(s"${isPresent(List(1, 2, 3, 4), 5)}")
+    println(s"${isPresent(List(1, 2, 3, 4), 3)}")
+    println("e)")
+    val l = List(List(1, 1), 2, List(3, List(5, 8)));
+    println(s"flattenList($l): ${flattenList(l)}")
+  }
+}