text: """
  Given string representing time in format of hh:mm some of digits are blank(?)
  Need to fill in the '?' => time represented by this string is the max possible
  
  "?4:5?"
  output: "14:59" 
  
      _  _ : _  _
      0  0   0  0
      1  .   .  .
      2  .   .  .
         9   5  9
  """
  
  def max_time(s:str):
      s = list(s)
      if s[0] == '?':
          s[0] = '2' if s[1] <= '3' or s[1] == '?' else '1'
      if s[1] == '?': s[1] = '9' if s[0] != '2' else '3'
      if s[3] == '?' : s[3] = '5'
      if s[4] == '?' : s[4] = '9'
  
      return ''.join(s) 
  
  print(max_time("?4:5?"))