Finding longest kaladont sequence

kaladont.rb

words = File.read("input.txt").split

def get(words, beginning, sequence)
  words[beginning].select { |word| !sequence.include?(word) } if words[beginning]
end

def kalodont(words, sequence)
  selected_words = get(words, sequence.last[-2..-1], sequence)

  if selected_words && !selected_words.empty?
    selected_words.each do |word|
      kalodont(words, sequence + [word])
    end
  elsif sequence.size > $max
    $max = sequence.size
    puts "******* NEW BIGGEST SEQUENCE WITH #{sequence.size} CHARACTERS *********"
    File.write("sequence.txt", sequence.join(" "))
  end
end

$max = 0

words_indexed_by_beginning = words.group_by { |word| word[0..1] }

words.each do |word|
  kalodont(words_indexed_by_beginning, [word])
end