bitmarine

d3.rb

test_input = %w[00100 11110 10110 10111 10101 01111 00111 11100 10000 11001 00010 01010]

# puzzle_input <<-BIN
#  # your puzzle input pasted here
# BIN

def most_common(list)
  count = list.tally
  if count.values.uniq.size == 1 # equal number of 1s and 0s
    '1'
  else
    count.max_by(&:last).first
  end
end

def gamma(input)
  columns = input.first.size
  matrix = input.map { |i| i.split('') }

  bits = []

  columns.times do |bit_column|
    bits << find_common(matrix.map {|b| b[bit_column]})
  end

  bits.join
end

def epsilon(g)
  ones = g.length.times.map{"1"}.join
  ("%0#{g.length}b" % (Integer("0b#{g}") ^ Integer("0b#{ones}")))
end

def power_output(binaries)
  gams = gamma(binaries)
  eps = epsilon(gams)
  Integer("0b#{eps}") * Integer("0b#{gams}")
end

#part 2 methods

def o2_info(input, but_which_o2: :c)
  columns = input.first.size
  matrix = input.map { |i| i.split('') }
  accepted = matrix.dup

  columns.times do |bit_column|
    bit = most_common(accepted.map{ |b| b[bit_column] })

    if but_which_o2 == :c
      accepted.reject! {|bs| bs[bit_column] == bit }
    else
      accepted.select! {|bs| bs[bit_column] == bit }
    end

    return accepted.join if accepted.size == 1
  end

  accepted.first.join # probably not necessary
end

def life_support(binaries)
  co2 = o2_info(binaries, but_which_o2: :c)
  o2 = o2_info(binaries, but_which_o2: :o)

  Integer("0b#{co2}") * Integer("0b#{o2}")
end

power_output puzzle_input # part 1 solution
life_support puzzle_input # part 2 solution