def duplicate_count(text)
    freq = {}
    letters = text.chars
    letters.each do |l|
      if freq.has_key? l
        freq[l] = freq[l] + 1
      else
        freq[l] = 1
      end
    end
  
    s = 0
  
    freq.each_value do |v|
      if v > 1
        s = s + 1
      end
    end
      
    s
end

puts duplicate_count 'aabc'