diff --git a/2022/README.md b/2022/README.md index 3aae86e..38fcbc5 100644 --- a/2022/README.md +++ b/2022/README.md @@ -2,7 +2,7 @@ My (attempted) solutions to [Advent of Code 2022](https://adventofcode.com/2022) in Elixir. -image +image ## Running: diff --git a/2022/day8.exs b/2022/day8.exs new file mode 100644 index 0000000..b36371d --- /dev/null +++ b/2022/day8.exs @@ -0,0 +1,130 @@ +defmodule Day8 do + defmodule Tree do + defstruct height: nil, visible: false, score: [] + end + + def part1({{max_x, max_y}, trees}) do + trees + |> look_in_direction(0..max_y, 0..max_x, false) + |> look_in_direction(0..max_x, 0..max_y, true) + |> look_in_direction(0..max_y, max_x..0, false) + |> look_in_direction(0..max_x, max_y..0, true) + |> Enum.count(&match?({_coord, %Tree{visible: true}}, &1)) + end + + defp look_in_direction(trees, outer_range, inner_range, flip_xy?) do + Enum.reduce(outer_range, trees, fn y, trees -> + {_height, trees} = + Enum.reduce_while(inner_range, {_height = -1, trees}, fn + _x, {9, trees} -> + {:halt, {9, trees}} + + x, {height, trees} -> + coord = if flip_xy?, do: {y, x}, else: {x, y} + tree = trees[coord] + + if tree.height > height do + {:cont, {tree.height, Map.replace(trees, coord, %Tree{tree | visible: true})}} + else + {:cont, {height, trees}} + end + end) + + trees + end) + end + + def part2({{max_x, max_y}, trees}) do + trees + |> count_viewing_distance(0..max_y, 0..max_x, false) + |> count_viewing_distance(0..max_x, 0..max_y, true) + |> count_viewing_distance(0..max_y, max_x..0, false) + |> count_viewing_distance(0..max_x, max_y..0, true) + |> Enum.map(fn {_coord, %Tree{score: score}} -> Enum.reduce(score, &Kernel.*/2) end) + |> Enum.max() + end + + defp count_viewing_distance(trees, outer_range, inner_range, flip_xy?) do + Enum.reduce(outer_range, trees, fn y, trees -> + {_scoring, trees} = + Enum.reduce(inner_range, {_scoring = [], trees}, fn + x, {scoring, trees} -> + coord = if flip_xy?, do: {y, x}, else: {x, y} + tree = trees[coord] + + {scoring, trees} = + Enum.reduce(scoring, {[], trees}, fn {coord, scoring_tree}, {scoring, trees} -> + %Tree{score: [score | scores]} = scoring_tree + scoring_tree = %Tree{scoring_tree | score: [score + 1 | scores]} + trees = Map.replace(trees, coord, scoring_tree) + + if scoring_tree.height <= tree.height do + {scoring, trees} + else + {[{coord, scoring_tree} | scoring], trees} + end + end) + + tree = %Tree{tree | score: [0 | tree.score]} + {[{coord, tree} | scoring], Map.replace(trees, coord, tree)} + end) + + trees + end) + end + + def input do + with [input_filename] <- System.argv(), + {:ok, input} <- File.read(input_filename) do + grid = + input + |> String.trim() + |> String.split("\n") + |> Enum.map(&String.graphemes/1) + + max_x = length(hd(grid)) - 1 + max_y = length(grid) - 1 + + trees = + for {row, y} <- Enum.with_index(grid), {height, x} <- Enum.with_index(row), into: %{} do + {{x, y}, %Tree{height: String.to_integer(height)}} + end + + {{max_x, max_y}, trees} + else + _ -> :error + end + end + + ####################### + # HERE BE BOILERPLATE # + ####################### + + def run do + case input() do + :error -> print_usage() + input -> run_parts_with_timer(input) + end + end + + defp run_parts_with_timer(input) do + run_with_timer(1, fn -> part1(input) end) + run_with_timer(2, fn -> part2(input) end) + end + + defp run_with_timer(part, fun) do + {time, result} = :timer.tc(fun) + IO.puts("Part #{part} (completed in #{format_time(time)}):\n") + IO.puts("#{result}\n") + end + + defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs" + defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms" + defp format_time(μsec), do: "#{μsec / 1_000_000}s" + + defp print_usage do + IO.puts("Usage: elixir day8.exs input_filename") + end +end + +Day8.run()