2023 Day 8 (Part2 doesn't complete)

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Adam Millerchip 2024-11-29 22:33:38 +09:00
parent 2169d4dc40
commit 4721839c46

86
2023/day8.exs Normal file
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defmodule Day8 do
def part1({instructions, network}) do
instructions
|> Stream.cycle()
|> Enum.reduce_while({"AAA", 0}, fn
_side, {"ZZZ", count} -> {:halt, count}
side, {node, count} -> {:cont, {elem(network[node], side), count + 1}}
end)
end
# Runs forever.
# Need a better answer. Start at the end and validate can get there or something?
def part2({instructions, network}) do
starting_nodes =
network
|> Map.keys()
|> Enum.filter(&match?(<<_::binary-2, "A">>, &1))
instructions
|> Stream.cycle()
|> Enum.reduce_while({starting_nodes, 0}, fn side, {current_nodes, count} ->
if Enum.all?(current_nodes, &match?(<<_::binary-2, "Z">>, &1)) do
{:halt, count}
else
next_nodes = Enum.map(current_nodes, fn node -> elem(network[node], side) end)
{:cont, {next_nodes, count + 1}}
end
end)
end
def input do
with [input_filename] <- System.argv(),
{:ok, input} <- File.read(input_filename) do
[instructions, nodes] = String.split(input, "\n\n")
instructions =
instructions
|> String.graphemes()
|> Enum.map(fn
"L" -> 0
"R" -> 1
end)
network =
for <<key::binary-3, " = (", left::binary-3, ", ", right::binary-3, ")\n" <- nodes>>,
into: %{},
do: {key, {left, right}}
{instructions, network}
else
_ -> :error
end
end
#######################
# 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("#{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 day8.exs input_filename")
end
end
Day8.run()