big_o.rb

word_chain = ['rap', 'trap', 'party', 'pastry']

exit unless word_chain.first.length === 3 # O(1)
result = word_chain.each_with_index do |word, index| # O(n)
  next if index == 0 # O(1)
  previous_word = word_chain[index - 1] # O(1)
  split_word = word.split(//) # O(1)
  split_previous_word = previous_word.split(//) # O(1)
  break unless split_word.length == split_previous_word.length + 1 # O(1)
  break unless (split_word - split_previous_word).length < 2 # O(1)
end

p result