input: Write a function to find the index of the largest number in a given list of integers. Return the index of the largest number. If the list is empty, return -1.
  assert find_largest_index([5, 10, 20, 6, 8])==2
  assert find_largest_index([1, 2, 3, 4, 5])==4
  assert find_largest_index([-1, -2, -3, -4, -5])==0
  assert find_largest_index([])==-1
output: def find_largest_index(lst):
      if not lst:
          return -1
      max_index = 0
      for i in range(1, len(lst)):
          if lst[i] > lst[max_index]:
              max_index = i
      return max_index