Best Time to Buy and Sell Stock III <leetcode>

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).

思路：这个题本来行到的分成两部分，分别用动态规划，后来在由于做第一个题的时候，看到过一个比较简单的动态规划，因此在这里直接用了，（虽然代码写的不同，想法不同，但是我们用的都是动态规划），一下比较简洁的动态规划的代码：

class Solution {
public:
    int maxProfit(vector<int> &prices) {
    int minl=INT_MAX;
    int maxr=INT_MIN;
    
    int size=prices.size();
    if(size==0)  return 0;
    vector<int> f1(size);
    vector<int> f2(size);
    
    minl=prices[0];
    
    for(int i=1;i<size;i++)
    {
        minl=min(minl,prices[i]);
        f1[i]=max(f1[i-1],prices[i]-minl);
    }
    
    maxr=prices[size-1];
    
    for(int i=size-2;i>=0;i--)
    {
       maxr=max(maxr,prices[i]); 
       f2[i]=max(f2[i+1],maxr-prices[i]);
    }
    
    int sum = 0;
        for (int i = 0; i < size; i++)
            sum = std::max(sum, f1[i] + f2[i]);

        return sum;
    }
};