Data commit

Task/Vampire-number/Elixir/vampire-number.elixir

@@ -0,0 +1,42 @@
+defmodule Vampire do
+  def factor_pairs(n) do
+    first = trunc(n / :math.pow(10, div(char_len(n), 2)))
+    last  = :math.sqrt(n) |> round
+    for i <- first .. last, rem(n, i) == 0, do: {i, div(n, i)}
+  end
+
+  def vampire_factors(n) do
+    if rem(char_len(n), 2) == 1 do
+      []
+    else
+      half = div(length(to_char_list(n)), 2)
+      sorted = Enum.sort(String.codepoints("#{n}"))
+      Enum.filter(factor_pairs(n), fn {a, b} ->
+        char_len(a) == half && char_len(b) == half &&
+        Enum.count([a, b], fn x -> rem(x, 10) == 0 end) != 2 &&
+        Enum.sort(String.codepoints("#{a}#{b}")) == sorted
+      end)
+    end
+  end
+
+  defp char_len(n), do: length(to_char_list(n))
+
+  def task do
+    Enum.reduce_while(Stream.iterate(1, &(&1+1)), 1, fn n, acc ->
+      case vampire_factors(n) do
+        [] -> {:cont, acc}
+        vf -> IO.puts "#{n}:\t#{inspect vf}"
+              if acc < 25, do: {:cont, acc+1}, else: {:halt, acc+1}
+      end
+    end)
+    IO.puts ""
+    Enum.each([16758243290880, 24959017348650, 14593825548650], fn n ->
+      case vampire_factors(n) do
+        [] -> IO.puts "#{n} is not a vampire number!"
+        vf -> IO.puts "#{n}:\t#{inspect vf}"
+      end
+    end)
+  end
+end
+
+Vampire.task