2024 day 05 solution ⭐ ⭐

lib/y2024/day_05.ex

@@ -0,0 +1,97 @@
+defmodule Aoc.Y2024.Day05 do
+  @moduledoc """
+  Solved https://adventofcode.com/2024/day/5
+  """
+  import Aoc.Helper.IO
+
+  def solve_part1(data), do: data |> process(%{}, []) |> sum_correct_order()
+  def solve_part2(data), do: data |> process(%{}, []) |> sum_incorrect_order()
+
+  def sum_correct_order([], _, result), do: result
+
+  def sum_correct_order([a | rest], order, result) do
+    if is_valid?(a, order) do
+      sum_correct_order(rest, order, result + Enum.at(a, div(length(a), 2)))
+    else
+      sum_correct_order(rest, order, result)
+    end
+  end
+
+  def sum_correct_order({list, order}), do: sum_correct_order(list, order, 0)
+
+  def process([], order, ins), do: {ins, order}
+
+  def process([[key, value] | data], order, ins),
+    do: process(data, Map.update(order, key, [value], fn existing -> Enum.sort([value | existing]) end), ins)
+
+  def process([a | data], order, ins), do: process(data, order, [a | ins])
+
+  def sum_incorrect_order([], _, result), do: result
+
+  def sum_incorrect_order([a | rest], order, result) do
+    if not is_valid?(a, order) do
+      sum_incorrect_order(rest, order, result + Enum.at(fix_list(a, order), div(length(a), 2)))
+    else
+      sum_incorrect_order(rest, order, result)
+    end
+  end
+
+  def sum_incorrect_order({list, order}), do: sum_incorrect_order(list, order, 0)
+
+  def fix_list(list, order) do
+    if not is_valid?(list, order) do
+      find_invalid_pair(list, order) |> swap(list) |> fix_list(order)
+    else
+      list
+    end
+  end
+  def find_invalid_pair(list, order) do
+    Enum.reduce_while(list, [], fn num, visited ->
+      if Map.has_key?(order, num) do
+        invalid_nums = Map.get(order, num, [])
+        invalids = Enum.filter(invalid_nums, &(&1 in visited))
+
+        if invalids != [] do
+          {:halt, List.first(invalids) |> then(fn x -> {x, num} end)}
+        else
+          {:cont, [num | visited]}
+        end
+      else
+        {:cont, [num | visited]}
+      end
+    end)
+  end
+
+  def is_valid?(list, order) do
+    Enum.reduce_while(list, {[], true}, fn num, {visited, is_valid} ->
+      if Map.has_key?(order, num) do
+        restricted = Map.get(order, num, [])
+
+        if Enum.any?(restricted, &(&1 in visited)) do
+          {:halt, {visited, false}}
+        else
+          {:cont, {[num | visited], is_valid}}
+        end
+      else
+        {:cont, {[num | visited], is_valid}}
+      end
+    end)
+    |> elem(1)
+  end
+
+  def swap({a, b}, list),
+    do:
+      list
+      |> List.update_at(Enum.find_index(list, fn x -> x == a end), fn _ -> b end)
+      |> List.update_at(Enum.find_index(list, fn x -> x == b end), fn _ -> a end)
+
+  def get_input() do
+    get_string_input("2024", "05")
+    |> String.split("\n", trim: true)
+    |> Enum.map(fn
+      x -> String.split(x, [",", "|"], trim: true) |> Enum.map(&String.to_integer/1)
+    end)
+  end
+
+  def solved_status(), do: :solved
+end

test/y2024/day_05_test.exs

@@ -0,0 +1,13 @@
+defmodule AocTest.Y2024.Day05Test do
+  @moduledoc false
+  use ExUnit.Case, async: true
+  import Aoc.Y2024.Day05
+
+  test "Part 1 is solved" do
+    assert solve_part1(get_input()) == 4569
+  end
+
+  test "Part 2 is solved" do
+    assert solve_part2(get_input()) == 6456
+  end
+end