85 lines
1.9 KiB
Elixir
85 lines
1.9 KiB
Elixir
defmodule Day6 do
|
|
def part1(input) do
|
|
input
|
|
|> run_days(80)
|
|
|> length()
|
|
end
|
|
|
|
defp run_days(school, 0), do: school
|
|
defp run_days(school, days), do: run_days(day(school), days - 1)
|
|
|
|
defp day(school), do: Enum.flat_map(school, &fish/1)
|
|
|
|
defp fish(0), do: [6, 8]
|
|
defp fish(age), do: [age - 1]
|
|
|
|
# Implementing part 2 completely differently to avoid exponential growth
|
|
|
|
def part2(input) do
|
|
counts = Map.new(0..8, fn age -> {age, 0} end)
|
|
|
|
input
|
|
|> Enum.frequencies()
|
|
|> Enum.into(counts)
|
|
|> run_days2(256)
|
|
|> Map.values()
|
|
|> Enum.sum()
|
|
end
|
|
|
|
defp run_days2(counts, 0), do: counts
|
|
defp run_days2(counts, days), do: run_days2(day2(counts), days - 1)
|
|
|
|
defp day2(counts) do
|
|
{breeders, counts} = Map.pop(counts, 0)
|
|
|
|
counts
|
|
|> Map.new(fn {age, count} -> {age - 1, count} end)
|
|
|> Map.update(6, 0, &(&1 + breeders))
|
|
|> Map.put(8, breeders)
|
|
end
|
|
|
|
def input do
|
|
with [input_filename] <- System.argv(),
|
|
{:ok, input} <- File.read(input_filename) do
|
|
input
|
|
|> String.trim()
|
|
|> String.split(",")
|
|
|> Enum.map(&String.to_integer/1)
|
|
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("#{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()
|