Advent of Code 2022 - Day 4

Day 4: Camp Cleanup

Description

Utils

defmodule Load do
  def file(path) do
    File.read!(__DIR__ <> path)
    |> String.split("\n", trim: true)
  end

  def string(value) do
    value |> String.split("\n", trim: true)
  end
end

Input

input = Load.file("/data/day04.txt")

Part 1

In how many assignment pairs does one range fully contain the other?

defmodule Part1 do
  def parse_pair([assignment1, assignment2]) do
    values1 = parse_assignment(assignment1)
    values2 = parse_assignment(assignment2)

    %{
      elf1: %{
        from: Enum.at(values1, 0),
        to: Enum.at(values1, 1)
      },
      elf2: %{
        from: Enum.at(values2, 0),
        to: Enum.at(values2, 1)
      }
    }
  end

  def assignments_overlapping?(pair) do
    %{
      elf1: %{from: from1, to: to1},
      elf2: %{from: from2, to: to2}
    } = pair

    cond do
      from1 <= from2 and to1 >= to2 -> true
      from1 >= from2 and to1 <= to2 -> true
      true -> false
    end
  end

  defp parse_assignment(group) do
    group
    |> String.split("-")
    |> Enum.map(&amp;String.to_integer/1)
  end
end

input
|> Enum.map(&amp;String.split(&amp;1, ","))
|> Enum.map(&amp;Part1.parse_pair/1)
|> Enum.map(&amp;Part1.assignments_overlapping?/1)
|> Enum.filter(&amp; &amp;1)
|> Enum.count()

Result

475

Part 2

In how many assignment pairs do the ranges overlap?

defmodule Part2 do
  def overlappint_at_all?(pair) do
    %{
      elf1: %{from: from1, to: to1},
      elf2: %{from: from2, to: to2}
    } = pair

    from1..to1
    |> Enum.any?(fn digit ->
      from2..to2 |> Enum.member?(digit)
    end)
  end
end

input
|> Enum.map(&String.split(&1, ","))
|> Enum.map(&Part1.parse_pair/1)
|> Enum.map(&Part2.overlappint_at_all?/1)
|> Enum.filter(& &1)
|> Enum.count()

Result

825