# HG changeset patch
# User Christian Urban <urbanc@in.tum.de>
# Date 1478601438 0
# Node ID ecf83084e41dc3b3e541b7f049ca986a35f63010
# Parent  714e60f22b17baa600b74599c73fbca4775215ca
updated

diff -r 714e60f22b17 -r ecf83084e41d progs/collatz_sol.scala
--- a/progs/collatz_sol.scala	Tue Nov 08 10:31:04 2016 +0000
+++ b/progs/collatz_sol.scala	Tue Nov 08 10:37:18 2016 +0000
@@ -1,12 +1,17 @@
 // Part 1 about the 3n+1 conceture
 //=================================
 
+//(1) Complete the collatz function below. It should
+//    recursively calculate the number of steps needed 
+//    until the collatz series reaches the number 1.
+//    If needed you can use an auxilary function that
+//    performs the recursion. The function should expect
+//    arguments in the range of 1 to 10 Million.
 
-//(1) Complete the collatz function below. It should
-//recursively calculates the number of steps needed 
-//number until a series ends with 1
-
-def collatz(n: Long): List[Long] = ...
+def collatz(n: Long): List[Long] =
+  if (n == 1) List(1) else
+    if (n % 2 == 0) (n::collatz(n / 2)) else 
+      (n::collatz(3 * n + 1))
 
 
 // an alternative that calculates the steps directly
@@ -16,12 +21,18 @@
       (1 + collatz1(3 * n + 1))
 
 
-//(2)
+//(2)  Complete the collatz bound function below. It should
+//     calculuate how many steps are needed for each number 
+//     from 1 upto a bound and return the maximum number of
+//     steps. You should expect bounds in the range of 1
+//     upto 10 million. 
+
 def collatz_max(bnd: Int): Int = {
   (for (i <- 1 to bnd) yield collatz(i).length).max
 }
 
 
+// some testing harness
 val bnds = List(10, 100, 1000, 10000, 100000, 1000000, 10000000)
 
 for (bnd <- bnds) {