79 lines
1.9 KiB
Elixir
79 lines
1.9 KiB
Elixir
#!/usr/bin/env elixir
|
|
defmodule Day11 do
|
|
def part1(stones) do
|
|
blink(stones, 25)
|
|
end
|
|
|
|
def part2(stones) do
|
|
blink(stones, 75)
|
|
end
|
|
|
|
def blink(stones, 0), do: stones |> Map.values() |> Enum.sum()
|
|
|
|
def blink(stones, times) do
|
|
stones
|
|
|> Enum.reduce(%{}, fn
|
|
{0, count}, next ->
|
|
Map.update(next, 1, count, &(&1 + count))
|
|
|
|
{stone, count}, next ->
|
|
string = Integer.to_string(stone)
|
|
size = byte_size(string)
|
|
|
|
if rem(size, 2) == 0 do
|
|
{a, b} = String.split_at(string, div(size, 2))
|
|
|
|
next
|
|
|> Map.update(String.to_integer(a), count, &(&1 + count))
|
|
|> Map.update(String.to_integer(b), count, &(&1 + count))
|
|
else
|
|
Map.update(next, stone * 2024, count, &(&1 + count))
|
|
end
|
|
end)
|
|
|> blink(times - 1)
|
|
end
|
|
|
|
def input do
|
|
with [input_filename] <- System.argv(),
|
|
{:ok, input} <- File.read(input_filename) do
|
|
input
|
|
|> String.split([" ", "\n"], trim: true)
|
|
|> Enum.map(&String.to_integer/1)
|
|
|> Enum.frequencies()
|
|
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 day11.exs input_filename")
|
|
end
|
|
end
|
|
|
|
Day11.run()
|