https://www.codewars.com/kata/recover-a-secret-string-from-random-triplets/ruby solution

recover_secret.rb

class Letter
  include Comparable

  attr_reader :before, :after
  def initialize(letter)
    @letter = letter
    @before = []
    @after = []
  end

  def <=>(other)
    @letter <=> other
  end

  def before?
    [email protected]?
  end

  def is_before(other)
    @before << other
    @before.uniq!
  end

  def after?
    [email protected]?
  end

  def is_after(other)
    @after << other
    @after.uniq!
  end

  def inspect
    "#<Letter(#@letter): before: #@before after: #@after>"
  end

  def to_str
    @letter
  end
end
 
class Triplets
  attr_reader :letters
  def initialize
    @letters = []
  end

  def add(first, sec, last)
    add_one first, sec, nil
    add_one sec, last, first
    add_one last, nil, sec
    self
  end

  def add_letter(letter)
    Letter.new(letter).tap { |let| @letters << let }
  end

  def find_letter(letter)
    return unless letter
    @letters.find(-> { add_letter letter }) { |l| l == letter }
  end

  def add_one(letter, before, after)
    letter = find_letter letter
    before = find_letter before
    after = find_letter after
    letter.is_before before if before
    letter.is_after after if after
  end

  def to_s
    @letters.reject(&:after?).tap do |res|
      res.push find_next_letter res.last until @letters.empty?
    end.join
  end

  def find_next_letter(letter)
    letter.before.find { |let| let.after == [letter] }.tap do
      letter.before.each { |bef| bef.after.delete letter }
      @letters.delete letter
    end
  end
end

def recover_secret(triplets)
  trips = triplets.reduce(Triplets.new) { |l, t| l.add(*t) }
  trips.to_s
end

triplets_1 = [
  ['t','u','p'],
  ['w','h','i'],
  ['t','s','u'],
  ['a','t','s'],
  ['h','a','p'],
  ['t','i','s'],
  ['w','h','s']
]

puts recover_secret triplets_1