solution2.5.2.10.scala provided

Signed-off-by: Andreas Roehler <andreas.roehler@online.de>

chapter02/worksheets/solution2.5.2.10.scala

@@ -0,0 +1,37 @@
+/** 
+  Exercise 2.5.2.10
+
+  Transform a given sequence xs: Seq[Int] into a sequence of type
+  Seq[(Int, Int)] of pairs that skip one neighbor.
+
+  Implement this transformation as a function skip1 with a type
+  parameter A instead of the type Int.
+
+  The required type signature and a sample test:
+
+  def skip1[A](xs: Seq[A]): Seq[(A, A)] = ???
+
+  scala> skip1(List(1, 2, 3, 4, 5))
+  res0: List[(Int, Int)] = List((1,3), (2,4), (3,5))
+  */
+
+def skip1Intern[A](xs: Seq[A], res: Seq[(A, A)] = Seq.empty): Seq[(A, A)] = {
+  if (xs.length < 3) res.reverse
+  else
+    skip1Intern(xs.tail, (xs.head, xs(2)) +: res)
+}
+
+def skip1[A](xs: Seq[A]): Seq[(A, A)] = {
+  skip1Intern[A](xs: Seq[A])
+}
+
+val expected: List[(Int, Int)] = List((1,3), (2,4), (3,5))
+val result =  skip1(List(1, 2, 3, 4, 5))
+assert(result == expected) 
+
+// scala> :load solution2.5.2.10.scala
+// :load solution2.5.2.10.scala
+// def skip1Intern[A](xs: Seq[A], res: Seq[(A, A)]): Seq[(A, A)]
+// def skip1[A](xs: Seq[A]): Seq[(A, A)]
+// val expected: List[(Int, Int)] = List((1,3), (2,4), (3,5))
+// val result: Seq[(Int, Int)] = List((1,3), (2,4), (3,5))