solution2.5.2.12.scala (#80)

* solution2.5.2.11.scala provided

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

* solution2.5.2.12.scala provided

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

---------

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

chapter02/worksheets/solution2.5.2.12.scala

@@ -0,0 +1,31 @@
+/** 
+  Exercise 2.5.2.12
+
+  Transform a sequence by removing adjacent repeated elements when
+  they are repeated more than 𝑘 times. Repetitions up to 𝑘 times
+  should remain unchanged.
+
+  The required type signature and a sample test:
+
+  def removeDups[A](s: Seq[A], k: Int): Seq[A] = ???
+
+  scala> removeDups(Seq(1, 1, 1, 1, 5, 2, 2, 5, 5, 5, 5, 5, 1), 3)
+  res0: Seq[Int] = List(1, 1, 1, 5, 2, 2, 5, 5, 5, 1)
+ */
+
+def removeDupsIntern[A](xs: Seq[A], k: Int, res: Seq[A] = Seq.empty): Seq[A] = { 
+  if (xs.isEmpty) res.reverse
+  else { 
+    val a: Seq[A] = xs.takeWhile(_ == xs.head).take(k)
+    val b =  xs.dropWhile(_ == xs.head)
+    removeDupsIntern(b, k, a ++ res)
+  }
+}
+
+def removeDups[A](s: Seq[A], k: Int): Seq[A] = {
+  removeDupsIntern(s, k)
+}
+
+val result = removeDups(Seq(1, 1, 1, 1, 5, 2, 2, 5, 5, 5, 5, 5, 1), 3)
+val expected: Seq[Int] = List(1, 1, 1, 5, 2, 2, 5, 5, 5, 1)
+assert(result == expected)