AdventOfCode/2022/day8.exs

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3.8 KiB
Elixir
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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()