Day 1

Section

sample = """
3   4
4   3
2   5
1   3
3   9
3   3
"""

defmodule Utils do
  def parse_input(input_text) do
    input_text
    |> String.split("\n", trim: true)
    |> Enum.map(&String.split(&1, " ", trim: true))
    |> List.zip
  end

  def load_text do
    File.read!("priv/day1.txt")
  end
end

Part 1

defmodule Part1 do
  def calc_diff({left_str, right_str}) do
    String.to_integer(left_str) - String.to_integer(right_str)
    |> abs
  end
end

sample
|> Utils.parse_input()
|> Enum.map(&(&1 |> Tuple.to_list() |> Enum.sort()))
|> List.zip()
|> Enum.map(&Part1.calc_diff/1)
|> Enum.sum()

File.cwd!()

Utils.load_text()
|> Utils.parse_input()
|> Enum.map(&(&1 |> Tuple.to_list() |> Enum.sort()))
|> List.zip()
|> Enum.map(&Part1.calc_diff/1)
|> Enum.sum()

Part 2

[left_groups, right_groups] =
  sample
  |> Utils.parse_input()
  |> Enum.map(fn row -> row |> Tuple.to_list() |> Enum.group_by(& &1) end)

left_groups
|> Enum.map(fn {key, val} ->
  right_list_count =
    (right_groups[key] || [])
    |> length

  String.to_integer(key) * length(val) * right_list_count
end)
|> Enum.sum

[left_groups, right_groups] =
  Utils.load_text()
  |> Utils.parse_input()
  |> Enum.map(fn row -> row |> Tuple.to_list() |> Enum.group_by(& &1) end)

left_groups
|> Enum.map(fn {key, val} ->
  right_list_count =
    (right_groups[key] || [])
    |> length

  String.to_integer(key) * length(val) * right_list_count
end)
|> Enum.sum