Advent Of Code 2021 - Day 8 Solution (Part 2)

solution.rb

# By far the most tedious puzzle to get the 2nd ⭐️
# Display class -> this is where most of the logic happens. Use different combinations of digit segments to determine
# the correct mapping

class Digit
  attr_accessor :segments, :length

  def initialize(raw)
    @raw = raw
    @segments = raw.split('') 
    @length = @segments.length
  end

  def is_1
    @length == 2
  end

  def is_7
    @length == 3
  end

  def is_4
    @length == 4
  end

  def is_8
    @length == 7
  end

  def is_2_3_5
    @length == 5
  end

  def is_0_6_9
    @length == 6
  end
end

class Output
  def initialize(raw)
    @raw = raw
    @segments = raw.split('') 
    @length = @segments.length
  end

  def value(mapping)
    extracted = extract_segments(mapping).sort
    
    return 0 if is_0(extracted)
    return 1 if is_1
    return 2 if is_2(extracted)
    return 3 if is_3(extracted)
    return 4 if is_4
    return 5 if is_5(extracted)
    return 6 if is_6(extracted)
    return 7 if is_7
    return 8 if is_8
    return 9 if is_9(extracted)
  end

  def extract_segments(mapping)
    mapping.select {|k,v| @segments.include?(k) }.values
  end

  def is_1
    @length == 2
  end

  def is_2(arr)
    arr == [1,3,4,5,7] 
  end

  def is_3(arr)
    arr == [1,3,4,6,7] 
  end

  def is_4
    @length == 4
  end

  def is_5(arr)
    arr == [1,2,4,6,7]
  end

  def is_6(arr)
    arr == [1,2,4,5,6,7]
  end

  def is_7
    @length == 3
  end

  def is_8
    @length == 7
  end

  def is_9(arr)
    arr == [1,2,3,4,6,7]
  end

  def is_0(arr)
    arr == [1,2,3,5,6,7]
  end
end

class Display
  def initialize(input, output)
    @digits = input.split(' ').map {|o| Digit.new(o) }
    @outputs = output.split(' ').map {|o| Output.new(o) }

    segment_two, segment_five = segment_two_and_five
    @mapping = {
     1 => segment_one,
     2 => segment_two,
     5 => segment_five
    }
    @mapping[4] = segment_four
    @mapping[7] = segment_seven
    @mapping[3] = segment_three
    @mapping[6] = segment_six
  end

  def decode
    inverted_mapping = @mapping.invert
    @outputs.map { |o| o.value(inverted_mapping).to_s }.join('').to_i
  end

  # Segment mapping
  #  111
  # 2   3
  #  444
  # 5   6
  #  777

  def segment_one
    seven = @digits.find(&:is_7)
    one = @digits.find(&:is_1)
    (seven.segments - one.segments).first
  end

  def segment_two_and_five
    grouped = @digits.find.select(&:is_2_3_5).map(&:segments).flatten.group_by(&:itself)
    singles = grouped.select { |k,v| v.length == 1 }.values.flatten
    five = singles - @digits.find(&:is_4).segments
    two = singles & @digits.find(&:is_4).segments
    return [two, five].flatten
  end

  def segment_four
    four = @digits.find(&:is_4)
    one = @digits.find(&:is_1)
    (four.segments - one.segments - [@mapping[2]]).first
  end

  def segment_seven
    eight = @digits.find(&:is_8)
    four = @digits.find(&:is_4)
    (eight.segments - [@mapping[1], @mapping[2], @mapping[4], @mapping[5]] - four.segments).first
  end

  def segment_three
    grouped = @digits.find.select(&:is_0_6_9).map(&:segments).flatten.group_by(&:itself)
    segment_3_4_5 = grouped.select { |k,v| v.length == 2 }.keys
    (segment_3_4_5 - [@mapping[4], @mapping[5]]).first
  end

  def segment_six
    one = @digits.find(&:is_1)
    (one.segments - [@mapping[3]]).first
  end
end

class Day8
  def self.run(inputs)
    values = inputs.split("\n").map do |line|
      display = Display.new(*line.split(' | '))
      display.decode
    end
    p values.sum
  end
end

Day8.run('be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe
edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc
fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg
fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb
aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea
fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb
dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe
bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef
egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb
gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce')