in ruby,

Write a method clever_char that accepts a string as an argument, the method should return array containging the characters of the string that appeared more than twice. the characters in returned array may be in any order.

clever_char("that's alright folks') #["t"]

clever_char("mississippi") # ["i", "s"]

clever_char("hot potato soup please") # ["o", "t", "" , "p"]

clever_char("runtime") # []