input: Write a function to calculate the maximum revenue that can be obtained from a list of stock prices. The function should return the maximum profit that can be made by buying and selling the stock once. If the given list is empty or contains only one price, the function should return 0.
  
  def max_revenue(prices):
      if len(prices) < 2:
          return 0
      min_price = prices[0]
      max_profit = 0
      for price in prices:
          if price < min_price:
              min_price = price
          else:
              max_profit = max(max_profit, price - min_price)
      return max_profit
  
  assert max_revenue([10, 7, 5, 8, 11, 9]) == 6
  assert max_revenue([7, 1, 5, 3, 6, 4]) == 5
  assert max_revenue([7, 6, 4, 3, 1]) == 0
  assert max_revenue([1]) == 0
  assert max_revenue([]) == 0
output: def max_revenue(prices):
      if len(prices) < 2:
          return 0
      min_price = prices[0]
      max_profit = 0
      for price in prices:
          if price < min_price:
              min_price = price
          else:
              max_profit = max(max_profit, price - min_price)
      return max_profit