Initial data commit

Task/Partition-function-P/Elixir/partition-function-p.elixir

@@ -0,0 +1,38 @@
+use Bitwise, skip_operators: true
+
+defmodule Partition do
+   def init(), do:
+      :ets.new :pN, [:set, :named_table, :private]
+
+   def gpentagonals(), do: Stream.unfold {1, 0}, &next/1
+   defp next({m, n}) do
+      a = case rem m, 2 do
+             0 -> div m, 2
+             1 -> m
+          end
+      {n, {m + 1, n + a}}
+   end
+
+   def p(0), do: 1
+   def p(n) do
+      case :ets.lookup :pN, n do
+         [{^n, val}] -> val
+         [] ->
+            {val, _} = gpentagonals()
+                       |> Stream.drop(1)
+                       |> Stream.take_while(fn m -> m <= n end)
+                       |> Stream.map(fn g -> p(n - g) end)
+                       |> Enum.reduce({0, 0},
+                              fn n, {a, sgn} -> {
+                                          a + (if sgn < 2, do: n, else: -n),
+                                          band(sgn + 1, 3)
+                                          }
+                              end)
+            :ets.insert :pN, {n, val}
+            val
+      end
+   end
+end
+
+Partition.init
+IO.puts Partition.p 6666