I’m pretty happy with my solutions so far, especially for Day 2 Part 2 I felt I was able to take advantage of a few things, especially a comprehension to structure it nicely:

I’m doing my problems in Elixir this year as well: http://github.com/sorentwo/aoc_2018

My solution today seems a little different from the others I’ve seen. I made use of String.myers_difference/2 for the second part:

  def common(addresses) do
    pairings = for add_a <- addresses, add_b <- addresses, add_a != add_b, do: {add_a, add_b}

    Enum.reduce_while(pairings, nil, fn {add_a, add_b}, _ ->
      case String.myers_difference(add_a, add_b) do
        [eq: _, del: << char :: size(8) >>, ins: _, eq: _] ->
          {:halt, String.replace(add_a, IO.chardata_to_string([char]), "")}

        _ -> {:cont, nil}
      end
    end)
  end

There are two other possible edit scripts that could have matched (first character or last character being the difference), but this worked for my inputs.