leetcode-121-买卖股票的最佳时机

class Solution(object):

    def maxProfit(self, prices):
        """
        :type prices: List[int]
        :rtype: int
        """
        if not len(prices):

            return 0

        m = prices[0]
        n = 0
        
        for val in prices:
            if val < m:
                m = val
            else:
                profit = val - m                       

            if profit > n:
                n = profit     
        return n