链接：121. 买卖股票的最佳时机 - 力扣（LeetCode）

维护到这天为止之前股票的最低价数组

 1 class Solution(object):
 2     def maxProfit(self, prices):
 3         """
 4         :type prices: List[int]
 5         :rtype: int
 6         """
 7         n = len(prices)
 8         min_prices = [10001] * n
 9         if n >=2 :
10             min_prices[1] = prices[0]
11         i = 2
12         while i < n:
13             min_prices[i] = min(min_prices[i-1], prices[i-1]) 
14             i += 1
15         res = 0
16         i = 1
17         while i < n:
18             res = max(res, prices[i]-min_prices[i])
19             i += 1
20         return res
21