Advent Of Code 2021 - Day 10 Solution (Part 2)

solution.rb

# Pretty simple challenge. The key is to loop through the string to keep finding instances of legal chucks and remove them.
# Chucks are made of itself so you can just keep removing the simplest chunks
class Line
  attr_reader :temp

  def initialize(raw)
    @raw = raw
    @temp = raw

    parse
  end
  
  def corrupted?
    @temp.include?(']') || @temp.include?(')') || @temp.include?('>') || @temp.include?('}')
  end

  def incomplete?
    !corrupted?
  end

  def first_incorrect_closing_char
    @temp.split('').each.with_index do |char, index|
      next if char == '{' || char == '[' || char == '<' || char == '('
      return char
    end
  end

  def score
    case first_incorrect_closing_char
    when ')' then 3
    when ']' then 57
    when '}' then 1197
    when '>' then 25137
    end
  end

  def closing_sequence
    @mirrored = []
    @temp.split('').reverse_each do |char| 
      case char
      when '(' then @mirrored.push(')')
      when '[' then @mirrored.push(']')
      when '{' then @mirrored.push('}')
      when '<' then @mirrored.push('>')
      end
    end
    @mirrored.join('')
  end

  def closing_sequence_score
    score = 0
    @mirrored.each do |char|
      score = score * 5
      case char
      when ')' then score = score + 1
      when ']' then score = score + 2
      when '}' then score = score + 3
      when '>' then score = score + 4
      end
    end
    return score
  end

  private

  def parse
    while @temp.include?('[]') || @temp.include?('<>') || @temp.include?('()') || @temp.include?('{}')
      @temp = @temp.split('[]').join('')
      @temp = @temp.split('<>').join('')
      @temp = @temp.split('()').join('')
      @temp = @temp.split('{}').join('')
    end
  end
end

class Day10
  def self.run(input)
    @lines = input.split("\n").map { |l| Line.new(l.strip) }
    scores = @lines.select(&:incomplete?).each(&:closing_sequence).map(&:closing_sequence_score)
    p scores.sort[scores.length / 2]
  end
end

Day10.run('[({(<(())[]>[[{[]{<()<>>
[(()[<>])]({[<{<<[]>>(
{([(<{}[<>[]}>{[]{[(<()>
(((({<>}<{<{<>}{[]{[]{}
[[<[([]))<([[{}[[()]]]
[{[{({}]{}}([{[{{{}}([]
{<[[]]>}<{[{[{[]{()[[[]
[<(<(<(<{}))><([]([]()
<{([([[(<>()){}]>(<<{{
<{([{{}}[<[[[<>{}]]]>[]]')