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2021 day 16 part 2

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Adam Millerchip 2022-11-30 19:16:45 +09:00
parent 84d40cce99
commit 13e154a0c2
1 changed files with 28 additions and 11 deletions
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39
2021/day16.exs
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@ -4,21 +4,17 @@ defmodule Day16 do
version_sum version_sum
end end
def part2(_input) do
:ok
end
@literal_type 4 @literal_type 4
@literal_part 1 @literal_part 1
@literal_end 0 @literal_end 0
@total_length_type 0 @total_length_type 0
@sub_packets_length_type 1 @sub_packets_length_type 1
def decode_packet(<<version::3, @literal_type::3, rest::bits>>, count, version_sum) do defp decode_packet(<<version::3, @literal_type::3, rest::bits>>, count, version_sum) do
decode_literal(rest, <<>>, count + 6, version_sum + version) decode_literal(rest, <<>>, count + 6, version_sum + version)
end end
def decode_packet(<<version::3, operator_type::3, rest::bits>>, count, version_sum) do defp decode_packet(<<version::3, operator_type::3, rest::bits>>, count, version_sum) do
{sub_packets, rest, count, version_sum} = {sub_packets, rest, count, version_sum} =
case rest do case rest do
<<@total_length_type::1, length::15, rest::bits>> -> <<@total_length_type::1, length::15, rest::bits>> ->
@ -45,21 +41,21 @@ defmodule Day16 do
{{:operator, operator_type, sub_packets}, rest, count, version_sum} {{:operator, operator_type, sub_packets}, rest, count, version_sum}
end end
def decode_literal(<<@literal_part::1, group::bits-4, rest::bits>>, acc, count, version_sum) do defp decode_literal(<<@literal_part::1, group::bits-4, rest::bits>>, acc, count, version_sum) do
decode_literal(rest, <<acc::bits, group::bits>>, count + 5, version_sum) decode_literal(rest, <<acc::bits, group::bits>>, count + 5, version_sum)
end end
def decode_literal(<<@literal_end::1, group::bits-4, rest::bits>>, acc, count, version_sum) do defp decode_literal(<<@literal_end::1, group::bits-4, rest::bits>>, acc, count, version_sum) do
literal_binary = <<acc::bits, group::bits>> literal_binary = <<acc::bits, group::bits>>
<<literal::size(bit_size(literal_binary))>> = literal_binary <<literal::size(bit_size(literal_binary))>> = literal_binary
{{:literal, literal}, rest, count + 5, version_sum} {{:literal, literal}, rest, count + 5, version_sum}
end end
def decode_sub_packets_by(_method, 0, decoded_packets, bits, count, version_sum) do defp decode_sub_packets_by(_method, 0, decoded_packets, bits, count, version_sum) do
{Enum.reverse(decoded_packets), bits, count, version_sum} {Enum.reverse(decoded_packets), bits, count, version_sum}
end end
def decode_sub_packets_by(method, remaining, decoded_packets, bits, count, version_sum) do defp decode_sub_packets_by(method, remaining, decoded_packets, bits, count, version_sum) do
{decoded_packet, rest, packet_size, version_sum} = decode_packet(bits, 0, version_sum) {decoded_packet, rest, packet_size, version_sum} = decode_packet(bits, 0, version_sum)
remaining = remaining =
@ -78,6 +74,27 @@ defmodule Day16 do
) )
end end
def part2(input) do
{packet, _rest, _count, _version_sum} = decode_packet(input, 0, 0)
evaluate(packet)
end
defp evaluate({:literal, literal}), do: literal
defp evaluate({:operator, op, args}) do
args
|> Enum.map(&evaluate/1)
|> calculate(op)
end
defp calculate(args, 0), do: Enum.sum(args)
defp calculate(args, 1), do: Enum.reduce(args, &Kernel.*/2)
defp calculate(args, 2), do: Enum.min(args)
defp calculate(args, 3), do: Enum.max(args)
defp calculate([a, b], 5), do: if(a > b, do: 1, else: 0)
defp calculate([a, b], 6), do: if(a < b, do: 1, else: 0)
defp calculate([a, b], 7), do: if(a == b, do: 1, else: 0)
def input do def input do
with [input_filename] <- System.argv(), with [input_filename] <- System.argv(),
{:ok, input} <- File.read(input_filename) do {:ok, input} <- File.read(input_filename) do
@ -120,4 +137,4 @@ defmodule Day16 do
end end
end end
# Day16.run() Day16.run()