Leetcode 123. Best Time to Buy and Sell Stock III

123. Best Time to Buy and Sell Stock III

• Total Accepted: 64481
• Total Submissions: 236301
• 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.

思路：DP，主要是状态的转移。

代码：为了节省内存，buy1写在sell1后面，buy2写在sell2后面

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int len=prices.size();
        //buy1:one buy  buy2:two buy,one sell
        //sell1:one buy,one sell  sell2:two buy,two sell
        int buy1=INT_MIN,buy2=INT_MIN,sell1=0,sell2=0;
        for(int i=0;i<len;i++){
            sell1=max(sell1,buy1+prices[i]);
            buy1=max(buy1,-prices[i]);
            sell2=max(sell2,buy2+prices[i]);
            buy2=max(buy2,sell1-prices[i]);
        }
        return max(sell1,sell2);
    }
};

参考：https://discuss.leetcode.com/topic/19750/my-c-solution-o-n-time-o-1-space-8ms