Day 5: Cafeteria

Day 5: Cafeteria

Day 5: Cafeteria

Part 1

defmodule AdventOfCode2025Day5Part1 do
  def run(input) do
    input
    |> parse_input()
    |> do_solve()
  end

  defp do_solve({ids, ranges}) do
    ids
    |> Enum.reduce(0, fn id, acc ->
      Enum.any?(ranges, fn range ->
        id in range
      end)
      |> if(do: acc + 1, else: acc)
    end)
  end

  defp parse_input(input) do
    [
      ranges,
      [""],
      ids,
      [""]
    ] = input
        |> String.split("\n")
        |> Enum.chunk_by(& &1 == "")
    
    ranges = Enum.map(ranges, fn range ->
              %{"first" => first, "last" => last} = Regex.named_captures(~r/(?\d*)-(?\d*)/, range)
              Range.new(String.to_integer(first), String.to_integer(last))
             end)
  
    ids = Enum.map(ids, &String.to_integer/1)
    
    {ids, ranges}
  end
end

test = """
3-5
10-14
16-20
12-18

1
5
8
11
17
32
"""

AdventOfCode2025Day5Part1.run(test)

Part 2

defmodule AdventOfCode2025Day5Part2 do
  def run(input) do
    input
    |> parse_input()
    |> solve()
  end

  defp solve({_ids, ranges}) do
    do_solve(ranges, 0, ranges)
    |> Enum.map(&Range.size/1)
    |> Enum.sum()
  end

  defp do_solve([], _offset, ranges), do: ranges

  defp do_solve([head | tail], offset, ranges) do
    if Enum.all?(tail, fn range -> Range.disjoint?(head, range) end) do
      do_solve(tail, offset + 1, ranges)
    else
      index = Enum.find_index(tail, fn range -> Range.disjoint?(head, range) == false end) + 1 + offset
      f1..l1//_ = Enum.at(ranges, index)
      f2..l2//_ = head
      new_ranges = List.replace_at(ranges, index, min(f1, f2)..max(l1, l2)) |> List.delete_at(offset)
      do_solve(new_ranges, 0, new_ranges)
    end
  end

  defp parse_input(input) do
    [
      ranges,
      [""],
      ids,
      [""]
    ] = input
        |> String.split("\n")
        |> Enum.chunk_by(& &1 == "")
    
    ranges = Enum.map(ranges, fn range ->
              %{"first" => first, "last" => last} = Regex.named_captures(~r/(?\d*)-(?\d*)/, range)
              Range.new(String.to_integer(first), String.to_integer(last))
             end)
  
    ids = Enum.map(ids, &String.to_integer/1)
    
    {ids, ranges}
  end
end

test = """
3-5
10-14
16-20
12-18

1
5
8
11
17
32
"""

AdventOfCode2025Day5Part2.run(test)