Data commit

Task/Hailstone-sequence/Elixir/hailstone-sequence.elixir

@@ -0,0 +1,23 @@
+defmodule Hailstone do
+  require Integer
+
+  def step(1)                        , do: 0
+  def step(n) when Integer.is_even(n), do: div(n,2)
+  def step(n)                        , do: n*3 + 1
+
+  def sequence(n) do
+    Stream.iterate(n, &step/1) |> Stream.take_while(&(&1 > 0)) |> Enum.to_list
+  end
+
+  def run do
+    seq27 = sequence(27)
+    len27 = length(seq27)
+    repr = String.replace(inspect(seq27, limit: 4) <> inspect(Enum.drop(seq27,len27-4)), "][", ", ")
+    IO.puts "Hailstone(27) has #{len27} elements: #{repr}"
+
+    {len, start} = Enum.map(1..100_000, fn(n) -> {length(sequence(n)), n} end) |> Enum.max
+    IO.puts "Longest sequence starting under 100000 begins with #{start} and has #{len} elements."
+  end
+end
+
+Hailstone.run