leetcode 123. Best Time to Buy and Sell Stock III

最新推荐文章于 2025-09-10 15:24:29 发布

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最新推荐文章于 2025-09-10 15:24:29 发布

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原文链接：http://www.cnblogs.com/njczy2010/p/5703761.html

本文介绍了一种使用动态规划算法解决股票交易中寻找最大利润的问题，特别针对允许进行最多两次交易的情况。通过前后两次动态规划过程，分别计算买低卖高的最大收益，最终找出全局最优解。

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123. Best Time to Buy and Sell Stock III

QuestionEditorial Solution

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Total Accepted: 62311
Total Submissions: 230292
Difficulty: Hard

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

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

Note:
You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).

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Array Dynamic Programming

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思路：

思想来源于动态规划，如果以arr[i]为第二个投资点，那么，必须找到i-1前面的最大投资收益

so，，，左右各dp一次。。。

 1 class Solution {
 2 public:
 3     int maxProfit(vector<int>& prices) {
 4         int sz = prices.size();
 5         vector<int> left(sz + 1,0);
 6         int i;
 7         int mi = INT_MAX;
 8         for(i = 0;i < sz;i++){
 9             if(i != 0){
10                 left[i] = left[i - 1];
11             }
12             if(prices[i] < mi){
13                 mi = prices[i];
14             }
15             else{
16                 left[i] = max(left[i],prices[i] - mi);
17             }
18         }
19         
20         vector<int> right(sz + 1,0);
21         int ma = INT_MIN;
22         for(i = sz - 1;i >= 0;i--){
23             if(i != sz - 1){
24                 right[i] = right[i + 1];
25             }
26             if(prices[i] > ma){
27                 ma = prices[i];
28             }
29             else{
30                 right[i] = max(right[i],ma - prices[i]);
31             }
32         }
33         //for(i = 0;i < sz;i++){
34         //    printf(" i = %d left = %d right = %d\n",i,left[i],right[i]);
35         //}
36         
37         int ma_profile = left[sz - 1];
38         for(i = 0;i < sz - 1;i++){
39             ma_profile = max(ma_profile,left[i] + right[i + 1]);
40         }
41         return ma_profile;
42     }
43 };