股票的最大利润

        给定一个数组，它的第 i 个元素是一支给定股票第 i 天的价格。如果你最多只允许完成一笔交易（即买入和卖出一支股票），设计一个算法来计算你所能获取的最大利润。注意你不能在买入股票前卖出股票。

def maxProfit(prices):
    if not prices or len(prices)<2:
        return 0
    min_p = prices[0]
    maxDiff = prices[1]-min_p
    for i in range(2,len(prices)):
        if prices[i-1]<min_p:
            min_p = prices[i-1]
        if prices[i]-min_p>maxDiff:
            maxDiff = prices[i]-min_p
    if maxDiff<0:
        return 0
    return maxDiff

动态规划

class Solution(object):
    def maxProfit(self, prices):
        min_p, max_p = 99999, 0
        for i in range(len(prices)):
            min_p = min(min_p, prices[i])
            max_p = max(max_p, prices[i]-min_p)
        return max_p