130 lines
3.8 KiB
Elixir
130 lines
3.8 KiB
Elixir
defmodule Day8 do
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defmodule Tree do
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defstruct height: nil, visible: false, score: []
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end
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def part1({{max_x, max_y}, trees}) do
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trees
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|> look_in_direction(0..max_y, 0..max_x, false)
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|> look_in_direction(0..max_x, 0..max_y, true)
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|> look_in_direction(0..max_y, max_x..0, false)
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|> look_in_direction(0..max_x, max_y..0, true)
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|> Enum.count(&match?({_coord, %Tree{visible: true}}, &1))
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end
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defp look_in_direction(trees, outer_range, inner_range, flip_xy?) do
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Enum.reduce(outer_range, trees, fn y, trees ->
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{_height, trees} =
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Enum.reduce_while(inner_range, {_height = -1, trees}, fn
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_x, {9, trees} ->
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{:halt, {9, trees}}
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x, {height, trees} ->
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coord = if flip_xy?, do: {y, x}, else: {x, y}
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tree = trees[coord]
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if tree.height > height do
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{:cont, {tree.height, Map.replace(trees, coord, %Tree{tree | visible: true})}}
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else
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{:cont, {height, trees}}
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end
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end)
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trees
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end)
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end
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def part2({{max_x, max_y}, trees}) do
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trees
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|> count_viewing_distance(0..max_y, 0..max_x, false)
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|> count_viewing_distance(0..max_x, 0..max_y, true)
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|> count_viewing_distance(0..max_y, max_x..0, false)
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|> count_viewing_distance(0..max_x, max_y..0, true)
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|> Enum.map(fn {_coord, %Tree{score: score}} -> Enum.reduce(score, &Kernel.*/2) end)
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|> Enum.max()
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end
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defp count_viewing_distance(trees, outer_range, inner_range, flip_xy?) do
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Enum.reduce(outer_range, trees, fn y, trees ->
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{_scoring, trees} =
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Enum.reduce(inner_range, {_scoring = [], trees}, fn
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x, {scoring, trees} ->
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coord = if flip_xy?, do: {y, x}, else: {x, y}
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tree = trees[coord]
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{scoring, trees} =
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Enum.reduce(scoring, {[], trees}, fn {coord, scoring_tree}, {scoring, trees} ->
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%Tree{score: [score | scores]} = scoring_tree
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scoring_tree = %Tree{scoring_tree | score: [score + 1 | scores]}
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trees = Map.replace(trees, coord, scoring_tree)
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if scoring_tree.height <= tree.height do
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{scoring, trees}
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else
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{[{coord, scoring_tree} | scoring], trees}
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end
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end)
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tree = %Tree{tree | score: [0 | tree.score]}
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{[{coord, tree} | scoring], Map.replace(trees, coord, tree)}
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end)
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trees
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end)
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end
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def input do
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with [input_filename] <- System.argv(),
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{:ok, input} <- File.read(input_filename) do
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grid =
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input
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|> String.trim()
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|> String.split("\n")
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|> Enum.map(&String.graphemes/1)
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max_x = length(hd(grid)) - 1
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max_y = length(grid) - 1
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trees =
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for {row, y} <- Enum.with_index(grid), {height, x} <- Enum.with_index(row), into: %{} do
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{{x, y}, %Tree{height: String.to_integer(height)}}
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end
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{{max_x, max_y}, trees}
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else
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_ -> :error
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end
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end
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#######################
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# HERE BE BOILERPLATE #
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#######################
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def run do
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case input() do
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:error -> print_usage()
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input -> run_parts_with_timer(input)
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end
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end
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defp run_parts_with_timer(input) do
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run_with_timer(1, fn -> part1(input) end)
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run_with_timer(2, fn -> part2(input) end)
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end
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defp run_with_timer(part, fun) do
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{time, result} = :timer.tc(fun)
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IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
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IO.puts("#{result}\n")
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end
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defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
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defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
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defp format_time(μsec), do: "#{μsec / 1_000_000}s"
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defp print_usage do
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IO.puts("Usage: elixir day8.exs input_filename")
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end
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end
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Day8.run()
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