2024 Day 1

Day 1: Historian Hysteria

Day 1: Historian Hysteria

Part 1

defmodule AdventOfCode2024Day1Part1 do
  def calculate_total_distance(left_list, right_list) do
    sorted_left = Enum.sort(left_list)
    sorted_right = Enum.sort(right_list)

    distances =
      Enum.zip(sorted_left, sorted_right)
      |> Enum.map(fn {left, right} -> abs(left - right) end)

    Enum.sum(distances)
  end

  def parse_input(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.map(fn line ->
      [left, right] = String.split(line, ~r/\s+/, trim: true)
      {String.to_integer(left), String.to_integer(right)}
    end)
    |> Enum.unzip()
  end
end

# テストデータ
input = """
3   4
4   3
2   5
1   3
3   9
3   3
"""

{left_list, right_list} = AdventOfCode2024Day1Part1.parse_input(input)

# 距離の計算
total_distance = AdventOfCode2024Day1Part1.calculate_total_distance(left_list, right_list)
IO.puts("Total distance: #{total_distance}")

Part 2

defmodule AdventOfCode2024Day1Part2 do
  def calculate_similarity_score(left_list, right_list) do
    right_counts = Enum.frequencies(right_list)

    Enum.reduce(left_list, 0, fn num, acc ->
      count = Map.get(right_counts, num, 0)
      acc + num * count
    end)
  end

  def parse_input(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.map(fn line ->
      [left, right] = String.split(line, ~r/\s+/, trim: true)
      {String.to_integer(left), String.to_integer(right)}
    end)
    |> Enum.unzip()
  end
end

# テストデータ
input = """
3   4
4   3
2   5
1   3
3   9
3   3
"""

{left_list, right_list} = AdventOfCode2024Day1Part2.parse_input(input)

# 類似度スコアの計算
similarity_score = AdventOfCode2024Day1Part2.calculate_similarity_score(left_list, right_list)
IO.puts("Similarity score: #{similarity_score}")