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16b_solution.rb
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16b_solution.rb
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input = File.read("16input.txt").strip
def hex2bits(hex)
hex.split("").flat_map do |h|
case h
when "0"
[0, 0, 0, 0]
when "1"
[0, 0, 0, 1]
when "2"
[0, 0, 1, 0]
when "3"
[0, 0, 1, 1]
when "4"
[0, 1, 0, 0]
when "5"
[0, 1, 0, 1]
when "6"
[0, 1, 1, 0]
when "7"
[0, 1, 1, 1]
when "8"
[1, 0, 0, 0]
when "9"
[1, 0, 0, 1]
when "A"
[1, 0, 1, 0]
when "B"
[1, 0, 1, 1]
when "C"
[1, 1, 0, 0]
when "D"
[1, 1, 0, 1]
when "E"
[1, 1, 1, 0]
when "F"
[1, 1, 1, 1]
else
raise "Invalid Hex Code"
end
end
end
def bits2int(bit_array)
bit_array.join.to_i(2)
end
def apply_op(operator, values)
case operator
when 0
values.sum
when 1
values.inject(1) { |a, e| a * e }
when 2
values.min
when 3
values.max
when 5
values[0] > values[1] ? 1 : 0
when 6
values[0] < values[1] ? 1 : 0
when 7
values[0] == values[1] ? 1 : 0
else
raise "bad op code"
end
end
# returns [value, remainder, processed]
# value = value of first package
# remainder = remaining bits after processing first package
# processed = number of bits processed for first package
def process_packet(bits)
type = bits2int(bits[3..5])
if type == 4
body = bits[6..]
remainder_start = 6
num_bits = []
body.each_slice(5) do |slice|
remainder_start += 5
num_bits += slice[1..]
if slice[0] == 0
break
end
end
[bits2int(num_bits), bits[remainder_start..], remainder_start]
else
sub_values = []
length_type = bits[6]
if length_type == 0
total_length = bits2int(bits[7..21])
remainder = bits[22..]
processed = 0
while processed < total_length
sub_value, remainder, sub_processed = process_packet(remainder)
sub_values << sub_value
processed += sub_processed
end
[apply_op(type, sub_values), remainder, processed+22]
else
packet_count = bits2int(bits[7..17])
remainder = bits[18..]
processed = 0
packet_count.times do
sub_value, remainder, sub_processed = process_packet(remainder)
sub_values << sub_value
processed += sub_processed
end
[apply_op(type, sub_values), remainder, processed+18]
end
end
end
sum, _, _ = process_packet(hex2bits(input))
puts sum