79 lines
1.7 KiB
Elixir
79 lines
1.7 KiB
Elixir
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#!/usr/bin/env elixir
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defmodule Day9 do
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def part1(histories) do
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histories
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|> Enum.map(&walk/1)
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|> Enum.sum()
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end
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def walk(history) do
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case Enum.uniq(history) do
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[last] -> last
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_ -> List.last(history) + walk(diff(history))
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end
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end
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def diff([_]), do: []
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def diff([a, b | rest]), do: [b - a | diff([b | rest])]
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def part2(histories) do
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histories
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|> Enum.map(&walk2/1)
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|> Enum.sum()
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end
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def walk2(history) do
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case Enum.uniq(history) do
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[first] -> first
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[first | _] -> first - walk2(diff(history))
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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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input
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|> String.split("\n", trim: true)
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|> Enum.map(fn line ->
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line
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|> String.split(" ")
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|> Enum.map(&String.to_integer/1)
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end)
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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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