leetcode-121-买股票的最佳时机

　题目描述;

方法一：O(n） O(1）

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        minprices = float('inf')
        maxprofit = 0
        for i in prices:
            if i<minprices:
                minprices = i
            elif i-minprices>maxprofit:
                maxprofit = i-minprices
        return maxprofit