Day15

Mix.install([
  {:kino_aoc, git: "https://github.com/ljgago/kino_aoc"},
  {:benchee, "~> 1.0"},
  {:nimble_parsec, "~> 1.0"},
  {:libgraph, "~> 0.16.0"},
  {:math, "~> 0.7.0"}
])

Get Input

{:ok, data} = KinoAOC.download_puzzle("2023", "15", System.fetch_env!("LB_AOC_SECRET"))

Solve

defmodule Day15 do
  def out(res, t), do: IO.puts("Res #{t}: #{res}")

  def run(data, :p1), do: data |> parse() |> solve1()
  def run(data, :p2), do: data |> parse() |> solve2()

  def parse(data) do
    data
    |> String.trim()
    |> String.split(",")
  end

  def hash(str) do
    str
    |> String.graphemes()
    |> Enum.reduce(0, fn <>, acc ->
      acc
      |> Kernel.+(code)
      |> Kernel.*(17)
      |> rem(256)
    end)
  end

  def hashmap({:ins, label, num}, boxes) do
    ind = hash(label)
    b = boxes[ind]

    nb =
      if Enum.find(b, fn {k, _v} -> k == label end) do
        Enum.reduce(b, [], fn {k, v}, acc ->
          (k == label &amp;&amp; [{label, num} | acc]) || [{k, v} | acc]
        end)
      else
        [{label, num} | Enum.reverse(b)]
      end

    Map.put(boxes, ind, Enum.reverse(nb))
  end

  def hashmap({:del, label, _}, boxes) do
    ind = hash(label)

    b =
      Enum.reduce(boxes[ind], [], fn {k, v}, acc ->
        (k == label &amp;&amp; acc) || [{k, v} | acc]
      end)

    Map.put(boxes, ind, Enum.reverse(b))
  end

  def get_op(str) do
    if String.contains?(str, "=") do
      [label, num] = String.split(str, "=", trim: true)
      {:ins, label, String.to_integer(num)}
    else
      {:del, String.trim(str, "-"), nil}
    end
  end

  def solve2(steps) do
    boxes = for i <- 0..255, into: %{}, do: {i, []}

    steps
    |> Enum.map(&amp;get_op/1)
    |> Enum.reduce(boxes, &amp;hashmap/2)
    |> Enum.reject(fn {_k, v} -> v == [] end)
    |> Enum.reduce(0, fn {ind, lens}, total ->
      lens
      |> Enum.with_index()
      |> Enum.reduce(total, fn {{_label, num}, l_ind}, total ->
        total + (1 + ind) * (l_ind + 1) * num
      end)
    end)
  end

  def solve1(steps) do
    steps
    |> Enum.map(&amp;hash/1)
    |> Enum.sum()
  end
end

td = """
rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7
"""

# 1320, 145
# 505379, 263211
td |> Day15.run(:p1) |> Day15.out("p1-test")
td |> Day15.run(:p2) |> Day15.out("p2-test")
data |> Day15.run(:p1) |> Day15.out("p1")
data |> Day15.run(:p2) |> Day15.out("p2")