91 lines
2.6 KiB
Elixir
91 lines
2.6 KiB
Elixir
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#!/usr/bin/env elixir
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defmodule Day3 do
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def part1(_input) do
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# for each number, check around its edges to see if there's a symbol
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fn {{x, y}, number, length}, acc ->
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top = for x <- (x - 1)..(x + length), do: {x, y - 1}
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bottom = for x <- (x - 1)..(x + length), do: {x, y + 1}
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box = [{x - 1, y}, {x + length, y}] ++ top ++ bottom
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if part_number?(box), do: [number | acc], else: acc
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end
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|> :ets.foldl(_acc = [], :numbers)
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|> Enum.sum()
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end
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def part_number?([]), do: false
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def part_number?([coord | rest]) do
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case :ets.lookup(:symbols, coord) do
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[_symbol] -> true
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[] -> part_number?(rest)
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end
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end
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def part2(_input) do
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:ok
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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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:ets.new(:numbers, [:named_table])
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:ets.new(:symbols, [:named_table])
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parse_schematic(input, _x = 0, _y = 0)
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else
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_ -> :error
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end
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end
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def parse_schematic("", _x, _y), do: :ok
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def parse_schematic("." <> rest, x, y), do: parse_schematic(rest, x + 1, y)
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def parse_schematic("\n" <> rest, _x, y), do: parse_schematic(rest, 0, y + 1)
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def parse_schematic(<<digit::utf8>> <> rest, x, y) when digit in ?0..?9 do
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{number, length, rest} = take_digits(<<digit::utf8>> <> rest, "", 0)
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:ets.insert(:numbers, {{x, y}, number, length})
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parse_schematic(rest, x + length, y)
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end
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def parse_schematic(<<symbol::utf8>> <> rest, x, y) do
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:ets.insert(:symbols, {{x, y}, <<symbol::utf8>>})
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parse_schematic(rest, x + 1, y)
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end
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def take_digits(<<digit::utf8>> <> rest, digits, count) when digit in ?0..?9,
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do: take_digits(rest, digits <> <<digit::utf8>>, count + 1)
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def take_digits(rest, digits, count), do: {String.to_integer(digits), count, rest}
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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 day3.exs input_filename")
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end
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end
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# Day3.run()
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