input: Write a function to find the index of the largest number in a list of integers. If the list is empty, return -1.
  def find_largest_index(nums):
      if not nums:
          return -1
      max_num = max(nums)
      return nums.index(max_num)
  
  assert find_largest_index([5, 10, 20, 6, 8]) == 2
  assert find_largest_index([3, 5, 7, 1, 9]) == 4
  assert find_largest_index([1]) == 0
  assert find_largest_index([]) == -1
output: def find_largest_index(nums):
      if not nums:
          return -1
      max_num = max(nums)
      return nums.index(max_num)