input: Write a Python function named `get_latest_time` that takes a string `s` representing a 12-hour format time where some of the digits (possibly none) are replaced with a "?". The time should be formatted as "HH:MM", where HH is between 00 and 11, and MM is between 00 and 59. Replace all the '?' characters in `s` with digits to form the latest valid 12-hour format time. The function should return the resulting string.
  
  Examples:
  - `s = "1?:?4"` should return `"11:54"`
  - `s = "0?:5?"` should return `"09:59"`
  
  Constraints:
  - The length of `s` is 5.
  - The character at `s[2]` is ":".
  - All characters except `s[2]` are digits or "?" characters.
  - The input guarantees there is at least one valid time between "00:00" and "11:59" after replacing the "?" characters.
output: def get_latest_time(s):
      if s[0] == '?':
          if s[1] == '?' or s[1] <= '1':
              s = '1' + s[1:]
          else:
              s = '0' + s[1:]
      if s[1] == '?':
          if s[0] == '1':
              s = s[0] + '1' + s[2:]
          else:
              s = s[0] + '9' + s[2:]
      if s[3] == '?':
          s = s[:3] + '5' + s[4:]
      if s[4] == '?':
          s = s[:4] + '9'
      return s