AdventOfCode/2022/day7.exs

141 lines
3.8 KiB
Elixir

defmodule Day7 do
@root ["/"]
@total_size 70_000_000
@space_needed 30_000_000
def part1(input) do
store = build_tree(input)
[@root]
|> build_queue([], store)
|> Enum.reduce(store, &update_dir_size/2)
|> Enum.filter(fn
{_k, {:dir, size, _paths}} -> size <= 100_000
_ -> false
end)
|> Enum.map(fn {_k, {_type, size, _paths}} -> size end)
|> Enum.sum()
end
def update_dir_size(path, store) do
{:dir, 0, paths} = Map.get(store, path)
size = store |> Map.take(paths) |> Enum.map(fn {_, {_, size, _}} -> size end) |> Enum.sum()
Map.put(store, path, {:dir, size, paths})
end
def build_queue([], queue, _store), do: queue
def build_queue([node | rest], queue, store) do
case Map.get(store, node) do
{:file, _size, nil} -> build_queue(rest, queue, store)
{:dir, _size, paths} -> build_queue(paths ++ rest, [node | queue], store)
end
end
def build_tree(input, path \\ [], store \\ %{})
def build_tree([], _path, store), do: store
def build_tree([{:cd, "/"} | rest], _path, store), do: build_tree(rest, @root, store)
def build_tree([{:cd, ".."} | rest], [_here | path], store), do: build_tree(rest, path, store)
def build_tree([{:cd, dir} | rest], path, store), do: build_tree(rest, [dir | path], store)
def build_tree([{:ls, items} | rest], path, store) do
# insert files into store with directory path
{paths, store} =
Enum.map_reduce(items, store, fn
{:dir, name}, store ->
item_path = [name | path]
{item_path, Map.put(store, item_path, {:dir, 0, []})}
{:file, size, name}, store ->
item_path = [name | path]
{item_path, Map.put(store, item_path, {:file, size, nil})}
end)
store = Map.put(store, path, {:dir, 0, paths})
build_tree(rest, path, store)
end
def part2(input) do
store = build_tree(input)
store =
[@root]
|> build_queue([], store)
|> Enum.reduce(store, &update_dir_size/2)
{:dir, space_used, _} = Map.get(store, @root)
unused_space = @total_size - space_used
space_to_free = @space_needed - unused_space
store
|> Enum.filter(&match?({_path, {:dir, _size, _paths}}, &1))
|> Enum.map(fn {_path, {:dir, size, _paths}} -> size end)
|> Enum.sort()
|> Enum.find(fn size -> size >= space_to_free end)
end
def input do
with [input_filename] <- System.argv(),
{:ok, input} <- File.read(input_filename) do
input
|> String.trim()
|> String.split("\n")
|> parse_input()
else
_ -> :error
end
end
def parse_input([]), do: []
def parse_input(["$ cd " <> dir | rest]), do: [{:cd, dir} | parse_input(rest)]
def parse_input(["$ ls" | rest]) do
{listings, rest} = Enum.split_while(rest, &(!match?("$" <> _, &1)))
listings =
Enum.map(listings, fn
"dir " <> dir ->
{:dir, dir}
file ->
[size, name] = String.split(file)
{:file, String.to_integer(size), name}
end)
[{:ls, listings} | parse_input(rest)]
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 day7.exs input_filename")
end
end
Day7.run()