input: Write a function to find the third largest element in a given list. If there are fewer than three unique elements, return None.
  def third_largest(lst):
      if len(lst) < 3:
          return None
      distinct = []
      for i in lst:
          if i not in distinct:
              distinct.append(i)
      distinct.sort(reverse=True)
      return distinct[2] if len(distinct) >= 3 else None
  
  assert third_largest([12, 13, 13, 45, 22, 99])==22
  assert third_largest([10, 20, 30, 40, 50, 60, 70])==50
  assert third_largest([1, 2, 2, 3, 3, 4])==2
  assert third_largest([1, 2])==None
  assert third_largest([1, 1, 1, 1, 1, 1, 1])==None
output: def third_largest(lst):
      if len(lst) < 3:
          return None
      distinct = []
      for i in lst:
          if i not in distinct:
              distinct.append(i)
      distinct.sort(reverse=True)
      return distinct[2] if len(distinct) >= 3 else None