LeetCode - 123. Best Time to Buy and Sell Stock III

 

 

Say you have an array for which the i.

Design an algorithm to find the maximum profit. You may complete at most two transactions.

Solution

动态规划法：用两个数组，数组f1[i]表示在[0, i]范围内进行一次买入卖出的最大收益，数组f2[i]表示在[i, n-1]范围内进行一次买入卖出的最大收益，则总的最大收益为max(f1[i]+f2[i])，数组f1、f2的求法参考题目121

python

 1 class Solution(object):
 2     def maxProfit(self, prices):
 3         """
 4         :type prices: List[int]
 5         :rtype: int
 6         """
 7         length = len(prices)
 8         if length <= 1:
 9             return 0
10 
11         f1 = []
12         f2 = []
13         min_price = prices[0]
14         f1.append(0)
15         for i in range(1, length):
16             min_price = min(min_price, prices[i])
17             f1.append(max(f1[i-1], prices[i]-min_price))
18 
19         # reverse the prices list to iterate them from behind
20         prices_re = prices
21         prices_re.reverse()
22         f2.append(0)
23         max_price = prices_re[0]
24         for i in range(1, length):
25             max_price = max(max_price, prices_re[i])
26             f2.append(max(f2[i-1], max_price-prices_re[i]))
27 
28         f2.reverse()
29         max_profit = 0
30         for i in range(length):
31             max_profit = max(max_profit, f1[i]+f2[i])
32 
33         return max_profit

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