AdventOfCode/2023/day3.exs

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Elixir
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2023-12-03 12:10:31 +00:00
#!/usr/bin/env elixir
defmodule Day3 do
def part1(_input) do
# for each number, check around its edges to see if there's a symbol
fn {{x, y}, number, length}, acc ->
top = for x <- (x - 1)..(x + length), do: {x, y - 1}
bottom = for x <- (x - 1)..(x + length), do: {x, y + 1}
box = [{x - 1, y}, {x + length, y}] ++ top ++ bottom
if part_number?(box), do: [number | acc], else: acc
end
|> :ets.foldl(_acc = [], :numbers)
|> Enum.sum()
end
def part_number?([]), do: false
def part_number?([coord | rest]) do
case :ets.lookup(:symbols, coord) do
[_symbol] -> true
[] -> part_number?(rest)
end
end
def part2(_input) do
:ok
end
def input do
with [input_filename] <- System.argv(),
{:ok, input} <- File.read(input_filename) do
:ets.new(:numbers, [:named_table])
:ets.new(:symbols, [:named_table])
parse_schematic(input, _x = 0, _y = 0)
else
_ -> :error
end
end
def parse_schematic("", _x, _y), do: :ok
def parse_schematic("." <> rest, x, y), do: parse_schematic(rest, x + 1, y)
def parse_schematic("\n" <> rest, _x, y), do: parse_schematic(rest, 0, y + 1)
def parse_schematic(<<digit::utf8>> <> rest, x, y) when digit in ?0..?9 do
{number, length, rest} = take_digits(<<digit::utf8>> <> rest, "", 0)
:ets.insert(:numbers, {{x, y}, number, length})
parse_schematic(rest, x + length, y)
end
def parse_schematic(<<symbol::utf8>> <> rest, x, y) do
:ets.insert(:symbols, {{x, y}, <<symbol::utf8>>})
parse_schematic(rest, x + 1, y)
end
def take_digits(<<digit::utf8>> <> rest, digits, count) when digit in ?0..?9,
do: take_digits(rest, digits <> <<digit::utf8>>, count + 1)
def take_digits(rest, digits, count), do: {String.to_integer(digits), count, rest}
#######################
# 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("#{inspect(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 day3.exs input_filename")
end
end
# Day3.run()