leetcode-121题:best time to buy and sell stock

class Solution:
    # @param {integer[]} prices
    # @return {integer}
    def maxProfit(self, prices):
        if prices==None or len(prices)==0:
            return 0
        cur_min = prices[0]
        max_profit = 0
        for price in prices:
            if price < cur_min:
                cur_min = price
            elif price-cur_min > max_profit:
                max_profit = price-cur_min
        return max_profit