Uloha PR1 - zkouska

test.rb

arr = %w(a ba ca)
letters = arr[0].split('').uniq

letters.length.times do |i|
  arr.slice(1, arr.length).each do |word|
    letters.delete(letters[i]) if letters[i] && !word.include?(letters[i])
  end
end

puts "pismena: #{letters.join(', ')}"