I’m new to Elixir (started yesterday) and as a first little program, I wanted to solve the Münchausen numbers problem.

“A Münchausen number is a number equal to the sum of its digits raised to each digit’s power. For instance, 3435 is a Münchausen number because 3^3+4^4+3^3+5^5 = 3435. The largest Münchausen number is less than 440 million.”

The problem is that my program eats up all my RAM (16 GB) and the OS kills the process. And I don’t understand what goes on with the garbage collector.

Here is my solution:

#!/usr/bin/env elixir

defmodule Munchausen do
  @cache [0] ++ for n <- 1..9, do: n ** n

  def get_cache(), do: @cache

  def explode(n), do: explode(n, [])

  # int, acc -> list[int]
  def explode(n, acc) when n == 0, do: acc

  def explode(n, acc) do
    digit = rem(n, 10)
    explode(div(n, 10), [digit | acc])
  end

  # int -> bool
  def is_munchausen(n) do
    digits = explode(n)
    li = for x <- digits, do: Enum.at(@cache, x)
    n == Enum.sum(li)
  end
end

defmodule Main do
  # @max 10_000
  @max 440_000_000

  def main() do
    # Munchausen.get_cache() |> IO.inspect
    for n <- 0..@max do
      # :erlang.garbage_collect()
      if rem(n, 1_000_000) == 0 do
        IO.puts("# #{n}")
      end
      if Munchausen.is_munchausen(n) do
        IO.puts(n)
      end
    end
  end
end

Main.main()

I know that it’s not optimal and slow. I’ll work on it.

Now the question is: why does it consume all my memory and how to prevent that? Thanks.