Day 15

lib/day15.ex

@@ -0,0 +1,32 @@
+defmodule Aoc2023.Day15 do
+  use Aoc2023
+
+  def parse(input) do
+    input |> String.split(",")
+  end
+
+  defp hash(str) do
+    for <<char <- str>>, reduce: 0 do
+      acc -> Bitwise.band((acc + char) * 17, 255) 
+    end
+  end
+
+  def part1(input) do
+    input |> Enum.map(&hash/1) |> Enum.sum
+  end
+
+  def part2(input) do
+    for instr <- input, reduce: 0..255 |> Enum.map(&{&1, []}) |> Enum.into(%{}) do
+      boxes ->
+        [_, label, op, lens] = Regex.run(~r/([a-z]+)([-=])(\d*)/, instr)
+        box = hash(label)
+        label = String.to_atom(label)
+        case op do
+          "=" -> boxes |> Map.update!(box, &Keyword.update(&1, label, String.to_integer(lens), fn _ -> String.to_integer(lens) end))
+          "-" -> boxes |> Map.update!(box, &Keyword.delete(&1, label))
+        end
+    end
+    |> Enum.flat_map(fn {box, lenses} -> lenses |> Enum.with_index(1) |> Enum.map(fn {{_, focus}, i} -> focus * (box + 1) * i end) end)
+    |> Enum.sum
+  end
+end

lib/mix_tasks.ex

@@ -16,6 +16,7 @@ defmodule Mix.Tasks.Aoc do
   defp module(12), do: Aoc2023.Day12
   defp module(13), do: Aoc2023.Day13
   defp module(14), do: Aoc2023.Day14
+  defp module(15), do: Aoc2023.Day15
   # [MODULE INSERTION POINT]  
 
   defp base_dir(), do: System.get_env("AOC_BASE")

tests/day15/1

@@ -0,0 +1 @@
+rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7

tests/day15/1.1

@@ -0,0 +1 @@
+1320

tests/day15/1.2

@@ -0,0 +1 @@
+145