solution2.5.2.2.scala provided

chapter02/worksheets/solution2.5.2.2.scala

@@ -0,0 +1,25 @@
+/** 
+  Exercise 2.5.2.2
+  Compute the Collatz sequence 𝑐𝑖 as a stream defined by
+  𝑐₀ = 𝑛 ;
+  𝑐 ₖ+₁ =
+           𝑐ₖ/2         if 𝑐ₖ is even,
+           3 ∗ 𝑐ₖ + 1   if 𝑐ₖ is odd.
+  Stop the stream when it reaches 1 (as one would expect5 it will).
+  */
+
+def collatzSequence(n: Int, xs: List[Int] = List(0)): List[Int] =
+  if (xs.head == 1) xs.init
+  else if (n % 2 == 0)
+       collatzSequence(n/2, n +: xs)
+  else collatzSequence (n * 3 + 1, n +: xs)
+
+val expected: List[Int] = List(1, 2, 4, 8)
+val result = collatzSequence(8)
+assert(result == expected)
+
+// scala> :load solution2.5.2.2.scala
+// :load solution2.5.2.2.scala
+// def collatzSequence(n: Int, xs: List[Int]): List[Int]
+// val expected: List[Int] = List(1, 2, 4, 8)
+// val result: List[Int] = List(1, 2, 4, 8)