Add Day 1 Part 2 and restructure stuff

Author: Linuus

README.md

@@ -1,3 +1,8 @@
 # AdventOfCode
 
-Run a specific day by executing e.g. `mix run AdventOfCode.Day01.exs`
+To run:
+
+```sh
+$ iex -S mix
+iex()> AdventOfCode.day01()
+```

lib/advent_of_code.ex

@@ -1,2 +1,7 @@
 defmodule AdventOfCode do
+  def day01 do
+    IO.puts "-- Day 01 --"
+    AdventOfCode.Day01.Part01.run()
+    AdventOfCode.Day01.Part02.run()
+  end
 end

lib/day01.exs renamed to lib/day01/part01.ex

@@ -1,22 +1,22 @@
-defmodule AdventOfCode.Day01 do
+defmodule AdventOfCode.Day01.Part01 do
   def run do
-    IO.puts "Inverse Captcha: #{solve()}"
+    IO.puts "Part 1: #{solve()}"
   end
 
-  def solve do
+  defp solve do
     input()
     |> String.codepoints()
     |> add_first_last()
     |> sum_if_adjacent(0)
   end
 
-  def sum_if_adjacent([_], sum), do: sum
-  def sum_if_adjacent([a, a | rest] = list, sum) do
+  defp sum_if_adjacent([_], sum), do: sum
+  defp sum_if_adjacent([a, a | rest], sum) do
     {int, ""} = Integer.parse(a)
     [a | rest]
     |> sum_if_adjacent(sum + int)
   end
-  def sum_if_adjacent([a, b | rest] = list, sum) do
+  defp sum_if_adjacent([_a, b | rest], sum) do
     [b | rest]
     |> sum_if_adjacent(sum)
   end
@@ -27,8 +27,6 @@ defmodule AdventOfCode.Day01 do
   end
 
   defp input do
-    "lib/inputs/day1_0.txt" |> File.read!() |> String.strip()
+    "lib/inputs/day1_0.txt" |> File.read!() |> String.trim()
   end
 end
-
-AdventOfCode.Day01.run()

lib/day01/part02.ex

@@ -0,0 +1,37 @@
+defmodule AdventOfCode.Day01.Part02 do
+  def run do
+    IO.puts "Part 2: #{solve()}"
+  end
+
+  defp solve do
+    input()
+    |> Enum.split(split_index(input()))
+    |> zip()
+    |> maybe_sum(0)
+    |> Kernel.*(2)
+  end
+
+  defp maybe_sum([], sum), do: sum
+  defp maybe_sum([{a, a} | t], sum) do
+    {a_int, ""} = Integer.parse(a)
+    maybe_sum(t, sum + a_int)
+  end
+  defp maybe_sum([_ | t], sum), do: maybe_sum(t, sum)
+
+  defp zip({first, last}) do
+    Enum.zip(first, last)
+  end
+
+  defp split_index(list) do
+    list
+    |> length()
+    |> div(2)
+  end
+
+  defp input do
+    "lib/inputs/day1_0.txt"
+    |> File.read!()
+    |> String.trim()
+    |> String.codepoints()
+  end
+end