input: Write a function to find the second largest element in a list.
  assert second_largest([10, 20, 4, 45, 99]) == 45
  assert second_largest([1, 2, 3, 4, 5]) == 4
  assert second_largest([50, 30, 20, 70, 90, 100]) == 90
output: def second_largest(lst):
      if len(lst) < 2:
          return None  # Return None if there are less than 2 elements
      first = second = float('-inf')
      for number in lst:
          if number > first:
              first, second = number, first
          elif number > second and number != first:
              second = number
      return second