input: from typing import List
  
  def third_largest(lst: List[int]) -> int:
      """
      Finds the third largest element in a given list of integers.
      If the list has fewer than 3 unique elements, returns None.
  
      >>> third_largest([12, 13, 13, 45, 22, 99])
      22
      >>> third_largest([5, 5, 4, 3])
      3
      >>> third_largest([1])
      None
      """
output:     if len(lst) < 3:
          return None
      unique_elements = list(set(lst))
      if len(unique_elements) < 3:
          return None
      unique_elements.sort(reverse=True)
      return unique_elements[2]