116 lines
3.3 KiB
Elixir
Executable file
116 lines
3.3 KiB
Elixir
Executable file
#!/usr/bin/env elixir
|
|
defmodule Patrol do
|
|
defstruct obstacles: MapSet.new(),
|
|
visited: MapSet.new(),
|
|
path: MapSet.new(),
|
|
x: 0,
|
|
y: 0,
|
|
max_x: nil,
|
|
max_y: nil,
|
|
dir_x: 0,
|
|
dir_y: -1
|
|
end
|
|
|
|
defmodule Day6 do
|
|
def part1(patrol), do: MapSet.size(patrol(patrol).visited)
|
|
|
|
def patrol(%Patrol{} = patrol) when patrol.x in [-1, patrol.max_x] or patrol.y in [-1, patrol.max_y] do
|
|
patrol
|
|
end
|
|
|
|
def patrol(%Patrol{} = patrol) do
|
|
next_x = patrol.x + patrol.dir_x
|
|
next_y = patrol.y + patrol.dir_y
|
|
|
|
patrol =
|
|
if MapSet.member?(patrol.obstacles, {next_x, next_y}) do
|
|
{dir_x, dir_y} = turn_right(patrol.dir_x, patrol.dir_y)
|
|
%Patrol{patrol | dir_x: dir_x, dir_y: dir_y}
|
|
else
|
|
visited = MapSet.put(patrol.visited, {patrol.x, patrol.y})
|
|
%Patrol{patrol | x: next_x, y: next_y, visited: visited}
|
|
end
|
|
|
|
next_path = {patrol.x, patrol.y, patrol.dir_x, patrol.dir_y}
|
|
|
|
if MapSet.member?(patrol.path, next_path) do
|
|
:loop
|
|
else
|
|
patrol = %Patrol{patrol | path: MapSet.put(patrol.path, next_path)}
|
|
patrol(patrol)
|
|
end
|
|
end
|
|
|
|
def turn_right(0, -1), do: {1, 0}
|
|
def turn_right(1, 0), do: {0, 1}
|
|
def turn_right(0, 1), do: {-1, 0}
|
|
def turn_right(-1, 0), do: {0, -1}
|
|
|
|
def part2(patrol) do
|
|
completed_patrol = patrol(patrol)
|
|
|
|
candidate_obstructions =
|
|
Enum.reduce(completed_patrol.visited, MapSet.new(), fn {x, y}, candidate_obstructions ->
|
|
Enum.into([{x - 1, y}, {x + 1, y}, {x, y - 1}, {x, y + 1}], candidate_obstructions)
|
|
end)
|
|
|
|
Enum.count(candidate_obstructions, fn {x, y} ->
|
|
new_obstacles = MapSet.put(patrol.obstacles, {x, y})
|
|
new_patrol = %Patrol{patrol | obstacles: new_obstacles}
|
|
|
|
patrol(new_patrol) == :loop
|
|
end)
|
|
end
|
|
|
|
def input do
|
|
with [input_filename] <- System.argv(),
|
|
{:ok, input} <- File.read(input_filename) do
|
|
{_x, max_x, max_y, {x, y}, obstacles} =
|
|
for <<char::binary-1 <- input>>, reduce: {0, 0, 0, nil, MapSet.new()} do
|
|
{x, max_x, y, guard, obstacles} ->
|
|
case char do
|
|
"." -> {x + 1, max_x, y, guard, obstacles}
|
|
"#" -> {x + 1, max_x, y, guard, MapSet.put(obstacles, {x, y})}
|
|
"^" -> {x + 1, max_x, y, {x, y}, obstacles}
|
|
"\n" -> {0, x, y + 1, guard, obstacles}
|
|
end
|
|
end
|
|
|
|
%Patrol{x: x, y: y, max_x: max_x, max_y: max_y, obstacles: obstacles}
|
|
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("#{inspect(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 day6.exs input_filename")
|
|
end
|
|
end
|
|
|
|
Day6.run()
|