--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pre_marking1/collatz.scala	Fri Nov 27 00:55:24 2020 +0000
@@ -0,0 +1,50 @@
+// Basic Part about the 3n+1 conjecture
+//==================================
+
+// generate jar with
+//   > scala -d collatz.jar  collatz.scala
+
+object CW6a { // for purposes of generating a jar
+
+def collatz(n: Long): Long =
+  if (n == 1) 0 else
+    if (n % 2 == 0) 1 + collatz(n / 2) else 
+      1 + collatz(3 * n + 1)
+
+
+def collatz_max(bnd: Long): (Long, Long) = {
+  val all = for (i <- (1L to bnd)) yield (collatz(i), i)
+  all.maxBy(_._1)
+}
+
+//collatz_max(1000000)
+//collatz_max(10000000)
+//collatz_max(100000000)
+
+/* some test cases
+val bnds = List(10, 100, 1000, 10000, 100000, 1000000)
+
+for (bnd <- bnds) {
+  val (steps, max) = collatz_max(bnd)
+  println(s"In the range of 1 - ${bnd} the number ${max} needs the maximum steps of ${steps}")
+}
+
+*/
+
+def is_pow(n: Long) : Boolean = (n & (n - 1)) == 0
+
+def is_hard(n: Long) : Boolean = is_pow(3 * n + 1)
+
+def last_odd(n: Long) : Long = 
+  if (is_hard(n)) n else
+    if (n % 2 == 0) last_odd(n / 2) else 
+      last_odd(3 * n + 1)
+
+
+//for (i <- 130 to 10000) println(s"$i: ${last_odd(i)}")
+//for (i <- 1 to 100) println(s"$i: ${collatz(i)}")
+
+}
+
+
+