Merge pull request #72 from andreas-roehler/master

solution2.5.2.4.scala provided

chapter02/worksheets/solution2.5.2.4.scala

@@ -0,0 +1,32 @@
+/** 
+  Exercise 2.5.2.4
+
+  For a, b, c of type Set[Int],
+  compute the set of all sets of the form Set(x, y, z)
+  where x is from a, y from b, and z from c.
+
+  The required type signature and a sample test:
+
+  def prod3(a: Set[Int], b: Set[Int], c: Set[Int]): Set[Set[Int]] = ???
+
+  scala> prod3(Set(1, 2), Set(3), Set(4, 5))
+  res0: Set[Set[Int]] = Set(Set(1,3,4), Set(1,3,5), Set(2,3,4), Set(2,3,5))
+
+  Hint: use flatMap.
+ */
+
+def prod3(a: Set[Int], b: Set[Int], c: Set[Int]): Set[Set[Int]] = {
+  val d =  List(a, b, c)
+  d(0).flatMap{ x => d(1).flatMap{ y => d(2).map{ z => Set(x, y, z) }}}
+}
+
+val result = prod3(Set(1, 2), Set(3), Set(4, 5))
+val expected: Set[Set[Int]] = Set(Set(1,3,4), Set(1,3,5), Set(2,3,4), Set(2,3,5)) 
+assert(result == expected)
+
+// scala> :load solution2.5.2.4.scala
+// :load solution2.5.2.4.scala
+// def prod3(a: Set[Int], b: Set[Int], c: Set[Int]): Set[Set[Int]]
+// val result: Set[Set[Int]] = Set(Set(1, 3, 4), Set(1, 3, 5), Set(2, 3, 4), Set(2, 3, 5))
+// val expected: Set[Set[Int]] = Set(Set(1, 3, 4), Set(1, 3, 5), Set(2, 3, 4), Set(2, 3, 5))
+