77 lines
1.8 KiB
Elixir
77 lines
1.8 KiB
Elixir
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#!/usr/bin/env elixir
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defmodule Day11 do
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def part1(stones) do
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1..25
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|> Enum.reduce(stones, fn _, stones -> blink(stones) end)
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|> Enum.count()
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end
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def blink([]), do: []
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def blink([0 | rest]), do: [1 | blink(rest)]
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def blink([stone | rest]) do
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string = Integer.to_string(stone)
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size = byte_size(string)
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if rem(size, 2) == 0 do
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string
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|> String.split_at(div(size, 2))
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|> Tuple.to_list()
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|> Enum.map(&String.to_integer/1)
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|> Kernel.++(blink(rest))
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else
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[stone |> Kernel.*(2024) | blink(rest)]
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end
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end
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# probably have to track the changes rather than keep the whole list?
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def part2(stones) do
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1..75
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|> Enum.reduce(stones, fn _, stones -> blink(stones) end)
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|> Enum.count()
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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.split([" ", "\n"], trim: true)
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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("#{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 day11.exs input_filename")
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end
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end
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Day11.run()
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