Advent of Code 2025 - Day 2 - Part 1 - Elixir

day02.ex

defmodule DAY02 do
  @moduledoc """
  Documentation for `Advent of Code 2025 Day 02 - module DAY02`.
  """

  @doc """

  ## Examples

      iex> DAY02.hello()
      :world

  """
  def part1(input) do
    input
    |> String.split(",")
    |> Enum.reduce([], fn range, acc ->
      range_split = range |> id_range
      range_split ++ acc
    end)
    |> Enum.reduce(0, fn curr_id, acc ->
      result = curr_id |> id_pattern()
      if result, do: acc + String.to_integer(curr_id), else: acc
    end)
  end

  def id_range(range) do
    [id_start, id_end] = range |> String.split("-")
    id_start = String.to_integer(id_start)
    id_end = String.to_integer(id_end)

    id_start..id_end
    |> Enum.to_list()
    |> Enum.map(&to_string/1)
  end

  def id_pattern(id) do
    len = id |> String.length()
    mid = len |> div(2)

    first_half = id |> String.slice(0, mid)
    second_half = id |> String.slice(mid, len - mid)

    first_half == second_half
  end

  def solve do
    read_input()
    |> part1

    # IO.puts("--- Part One ---")
    # IO.puts("Result: #{part1(input)}")
  end

  defp read_input do
    File.read!("./inputs/input.txt")
  end
end