116 lines
3.4 KiB
Elixir
Executable file
116 lines
3.4 KiB
Elixir
Executable file
#!/usr/bin/env elixir
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defmodule Day9 do
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def part1(input) do
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{size, _, spaces, _, disk, files} =
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Enum.reduce(input, {0, 0, 0, true, %{}, []}, fn len,
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{idx, id, spaces, file?, disk, files} ->
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if file? do
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disk = Enum.into(idx..(idx + len - 1), disk, fn i -> {i, id} end)
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files = if file?, do: for(_ <- 1..len, do: id) ++ files, else: files
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{idx + len, id + 1, spaces, not file?, disk, files}
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else
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{idx + len, id, spaces + len, not file?, disk, files}
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end
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end)
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for i <- 0..(size - spaces - 1), reduce: {0, files} do
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{checksum, files} ->
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case Map.fetch(disk, i) do
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{:ok, block} ->
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{checksum + block * i, files}
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:error ->
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[block | files] = files
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{checksum + block * i, files}
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end
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end
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|> elem(0)
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end
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# Super inefficient, but this is the 2nd attempt after trying to be more efficient
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# worked on the sample but not the actual input
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def part2(input) do
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{_, _, _, disk, files} =
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Enum.reduce(input, {0, 0, true, %{}, []}, fn len, {idx, id, file?, disk, files} ->
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if file? do
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disk = Map.put(disk, idx, {:file, id, len})
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files = [{idx, id, len} | files]
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{idx + len, id + 1, not file?, disk, files}
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else
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disk = Map.put(disk, idx, {:space, len})
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{idx + len, id, not file?, disk, files}
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end
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end)
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Enum.reduce(files, disk, fn {idx, id, len}, disk ->
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# This scans the disk every time. Could possibly optimise by storing the known
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# eligible spaces separately
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case Enum.find(0..(idx - 1), &match?({:space, gap} when gap >= len, disk[&1])) do
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nil ->
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disk
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space_idx ->
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{:space, spaces} = Map.fetch!(disk, space_idx)
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disk = disk |> Map.delete(idx) |> Map.put(space_idx, {:file, id, len})
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remainder_spaces = spaces - len
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if remainder_spaces > 0 do
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Map.put(disk, space_idx + len, {:space, remainder_spaces})
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else
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disk
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end
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end
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end)
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|> Enum.reduce(0, fn
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{_idx, {:space, _}}, checksum ->
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checksum
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{idx, {:file, id, len}}, checksum ->
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for idx <- idx..(idx + len - 1), reduce: checksum do
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checksum -> checksum + idx * id
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end
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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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for <<c::binary-1 <- String.trim_trailing(input, "\n")>>, do: String.to_integer(c)
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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("#{inspect(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 day9.exs input_filename")
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end
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end
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Day9.run()
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