[LeetCode] Best Time to Buy and Sell Stock III

Say you have an array for which the i^th 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).

class Solution {
public:
    int maxProfit(vector<int> &prices) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (prices.size() == 0)
            return 0;
            
        vector<int> f1(prices.size());
        vector<int> f2(prices.size());
        
        int minV = prices[0];
        f1[0] = 0;
        for(int i = 1; i < prices.size(); i++)
        {
            minV = min(minV, prices[i]);
            f1[i] = max(f1[i-1], prices[i] - minV);
        }
        
        int maxV = prices[prices.size()-1];
        f2[f2.size()-1] = 0;
        for(int i = prices.size() - 2; i >= 0; i--)
        {
            maxV = max(prices[i], maxV);
            f2[i] = max(f2[i+1], maxV - prices[i]);
        }
        
        int sum = 0;
        for(int i = 0; i < prices.size(); i++)
            sum = max(sum, f1[i] + f2[i]);
            
        return sum;
    }
};