#買賣股票的最佳時機 III
class Solution:

    def maxProfit(self, prices):
        n = len(prices)
        if n <= 1: return 0
        p1 = [0] * n #p1=[0,0,0,0,...,0]
        p2 = [0] * n
        
        minV = prices[0]
        for i in range(1,n):
            minV = min(minV, prices[i])       # Find low and buy low
            p1[i] = max(p1[i - 1], prices[i] - minV)
        
        maxV = prices[-1]
        for i in range(n-2, -1, -1):
            maxV = max(maxV, prices[i])     # Find high and sell high
            p2[i] = max(p2[i + 1], maxV - prices[i])
        
        res = 0
        for i in range(n):
            res = max(res, p1[i] + p2[i])
        return res