121Best Time to Buy and Sell Stock

class Solution(object):
    def maxProfit(self, prices):
        """
        :type prices: List[int]
        :rtype: int
        """
        if not prices or len(prices)==0:
            return 0
        profit=0
        min_price=prices[0]
        for i in range(1,len(prices)):
            profit=max(profit,prices[i]-min_price)
            min_price=min(min_price,prices[i])

        return profit

记录买入最小值

记录每一步的最大利润

最大利润为当前值减去最小值