2016 Update

Task/Stern-Brocot-sequence/Elixir/stern-brocot-sequence.elixir

@@ -0,0 +1,28 @@
+defmodule SternBrocot do
+  def sequence do
+    Stream.unfold({0,{1,1}}, fn {i,acc} ->
+      a = elem(acc, i)
+      b = elem(acc, i+1)
+      {a, {i+1, Tuple.append(acc, a+b) |> Tuple.append(b)}}
+    end)
+  end
+
+  def task do
+    IO.write "First fifteen members of the sequence:\n  "
+    IO.inspect Enum.take(sequence, 15)
+    Enum.each(Enum.concat(1..10, [100]), fn n ->
+      i = Enum.find_index(sequence, &(&1==n)) + 1
+      IO.puts "#{n} first appears at #{i}"
+    end)
+    Enum.take(sequence, 1000)
+    |> Enum.chunk(2,1)
+    |> Enum.all?(fn [a,b] -> gcd(a,b) == 1 end)
+    |> if(do: "All GCD's are 1", else: "Whoops, not all GCD's are 1!")
+    |> IO.puts
+  end
+
+  defp gcd(a,0), do: abs(a)
+  defp gcd(a,b), do: gcd(b, rem(a,b))
+end
+
+SternBrocot.task