121. Best Time to Buy and Sell Stock

问题描述

Say you have an array for which the ith element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Note that you cannot sell a stock before you buy one.

思路

1. 记录两个值，min_price【代码中用p表示】和max_profit【代码中用pf表示】
2. 用for loop过一遍list，对于每个新的元素：

• 如果小于min_price，则不可能创造新的max_profit，于是只更新min_price
• 如果不是新的min_price，则有可能创造新的max_profit，于是对比当前数字cur_price - min_price 与max_profit的值，若大于max_profit，更新max_profit

3. 返回max_profit

    def maxProfit(self, prices):
        """
        :type prices: List[int]
        :rtype: int
        """
        pf = 0
        p = 999999999
        
        for i in range (0, len(prices)):
            if prices[i] < p:
                p = prices[i]
            elif prices[i]-p > pf:
                pf = prices[i]-p
            
        return pf