[TASK] Day 2, part 1 in Elixir

day2-elixir/lib/day2.ex

@@ -0,0 +1,30 @@
+defmodule Day2 do
+  @moduledoc """
+  Documentation for `Day2`.
+  """
+  require Integer
+
+  def start(_type, _args) do
+
+    input_file = File.read("input/day2.txt")
+    IO.puts "Part 1: #{Day2.part1(elem(input_file, 1))}"
+  end
+
+  def part1(input) do
+    for range <- String.split(input, ",") do
+      [from, to] = String.split(range, "-") |> Enum.map(fn s -> String.to_integer(s) end)
+      eval_range(from, to)
+    end |> Enum.sum
+  end
+
+  def eval_range(from, to) do
+    Enum.filter(from..to, fn x -> is_valid_id(x) end) |> Enum.sum
+  end
+
+  def is_valid_id(id) do
+    digit_count = Enum.count(Integer.digits(id))
+    power = 10 ** (div(digit_count, 2))
+    # IO.inspect {id, digit_count, power, div(id, power), rem(id, power)}
+    Integer.is_even(digit_count) && div(id, power) == rem(id, power)
+  end
+end