string_constitutes_of.rb

class String
  def constitutes_of?(phrases)
    _constitutes_of?(phrases.sort_by!(&:length))
  end

  protected

  def _constitutes_of?(phrases)
    return false if phrases.empty?

    absent_phrases = []

    phrases.each do |phrase|
      remainders = []
      if (i = index(phrase))
        remainders << self[0..i-1] if i > 0
        remainders << self[i+phrase.length..-1]
      else
        absent_phrases << phrase
        next
      end

      remainders.sort_by!(&:length)
      phrases_left = phrases - absent_phrases

      return true if remainders.all? { |r| r.empty? || r._constitutes_of?(phrases_left) }
    end

    false
  end
end