从前往后遍历：
python
class Solution:
def maxProfit(self, prices: List[int]) -> int:
if (len(prices)==1):
return 0
max_profit = 0
min_price = float('inf')
for i in range(len(prices)):
if prices[i] < min_price:
min_price = prices[i]
if max_profit < (prices[i]-min_price):
max_profit = prices[i]-min_price
return max_profit
