Merge pull request #59 from andreas-roehler/master

solution2.2.6.2 provided

chapter02/worksheets/solution2.2.6.2.scala

@@ -0,0 +1,35 @@
+/** 
+  Exercise 2.2.6.2
+  Implement the flatten method for sequences by using foldLeft.
+
+  The required type signature and a sample test are:
+
+  def flatten[A](xxs: Seq[Seq[A]]): Seq[A] = ???
+
+  scala> flatten(Seq(Seq(1, 2, 3), Seq(), Seq(4)))
+  res0: Seq[Int] = List(1, 2, 3, 4)
+
+  scala> flatten(Seq(Seq("a","b"), Seq(), (Seq("c","<nothing>"))))
+  val res1: Seq[String] = List(a, b, c, <nothing>)
+  */
+
+def flatten[A](xxs: Seq[Seq[A]]): Seq[A] = { 
+  var init: Seq[A] = Seq()
+  xxs.foldLeft(init){ (x, y) => y.foreach( k => (init = init :+ k)); init}
+}
+
+val result = flatten(Seq(Seq(1, 2, 3), Seq(), Seq(4)))
+val expected: Seq[Int] = List(1, 2, 3, 4)
+assert(result == expected)
+
+val a = flatten(Seq(Seq("a","b"), Seq(), (Seq("c","<nothing>"))))
+val b: Seq[String] = List("a", "b", "c", "<nothing>")
+assert(a == b)
+
+// scala> :load solution2.2.6.2.scala
+// :load solution2.2.6.2.scala
+// def flatten[A](xxs: Seq[Seq[A]]): Seq[A]
+// val result: Seq[Int] = List(1, 2, 3, 4)
+// val expected: Seq[Int] = List(1, 2, 3, 4)
+// val a: Seq[String] = List(a, b, c, <nothing>)
+// val b: Seq[String] = List(a, b, c, <nothing>)

chapter02/worksheets/solution2.2.6.2_main.scala

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+/** 
+  Exercise 2.2.6.2
+  Implement the flatten method for sequences by using foldLeft.
+
+  The required type signature and a sample test are:
+
+  def flatten[A](xxs: Seq[Seq[A]]): Seq[A] = ???
+
+  scala> flatten(Seq(Seq(1, 2, 3), Seq(), Seq(4)))
+  res0: Seq[Int] = List(1, 2, 3, 4)
+
+  scala> flatten(Seq(Seq("a","b"), Seq(), (Seq("c","<nothing>"))))
+  val res1: Seq[String] = List(a, b, c, <nothing>)
+  */
+
+object Flatten {
+  def flatten[A](xxs: Seq[Seq[A]]): Seq[A] = {
+    var init: Seq[A] = Seq()
+      xxs.foldLeft(init){ (x, y) => y.foreach( k => (init = init :+ k)); init}
+  }
+  def main(args: Array[String]): Unit = {
+
+    val result = flatten(Seq(Seq(1, 2, 3), Seq(), Seq(4)))
+    val expected: Seq[Int] = List(1, 2, 3, 4)
+    println("result: %s".format(result))
+    println("expected: %s".format(expected))
+    assert(result == expected)
+
+    val a = flatten(Seq(Seq("a","b"), Seq(), (Seq("c","<nothing>"))))
+    val b: Seq[String] = List("a", "b", "c", "<nothing>")
+    println("a: %s".format(a))
+    println("b: %s".format(b))
+
+    assert(a == b)
+  }
+}
+
+Flatten.main(Array())
+
+// scala> :load solution2.2.6.2_main.scala
+// :load solution2.2.6.2_main.scala
+// result: List(1, 2, 3, 4)
+// expected: List(1, 2, 3, 4)
+// a: List(a, b, c, <nothing>)
+// b: List(a, b, c, <nothing>)
+// // defined object Flatten