84 lines
1.9 KiB
Elixir
84 lines
1.9 KiB
Elixir
defmodule Day6 do
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def part1(input) do
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input
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|> run_days(80)
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|> length()
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end
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defp run_days(school, 0), do: school
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defp run_days(school, days), do: run_days(day(school), days - 1)
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defp day(school), do: Enum.flat_map(school, &fish/1)
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defp fish(0), do: [6, 8]
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defp fish(age), do: [age - 1]
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# Implementing part 2 completely differently to avoid exponential growth
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def part2(input) do
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counts = Map.new(0..8, fn age -> {age, 0} end)
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input
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|> Enum.frequencies()
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|> Enum.into(counts)
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|> run_days2(256)
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|> Map.values()
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|> Enum.sum()
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end
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defp run_days2(counts, 0), do: counts
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defp run_days2(counts, days), do: run_days2(day2(counts), days - 1)
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defp day2(counts) do
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{breeders, counts} = Map.pop(counts, 0)
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counts
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|> Map.new(fn {age, count} -> {age - 1, count} end)
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|> Map.update(6, 0, &(&1 + breeders))
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|> Map.put(8, breeders)
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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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input
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|> String.trim()
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|> String.split(",")
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|> Enum.map(&String.to_integer/1)
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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("#{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 day6.exs input_filename")
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end
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end
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Day6.run()
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