[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).

 1 class Solution {

 2 public:

 3     int maxProfit(vector<int> &prices) {

 4         // Start typing your C/C++ solution below

 5         // DO NOT write int main() function

 6         if (prices.size() == 0)

 7             return 0;

 8             

 9         vector<int> f1(prices.size());

10         vector<int> f2(prices.size());

11         

12         int minV = prices[0];

13         f1[0] = 0;

14         for(int i = 1; i < prices.size(); i++)

15         {

16             minV = min(minV, prices[i]);

17             f1[i] = max(f1[i-1], prices[i] - minV);

18         }

19         

20         int maxV = prices[prices.size()-1];

21         f2[f2.size()-1] = 0;

22         for(int i = prices.size() - 2; i >= 0; i--)

23         {

24             maxV = max(prices[i], maxV);

25             f2[i] = max(f2[i+1], maxV - prices[i]);

26         }

27         

28         int sum = 0;

29         for(int i = 0; i < prices.size(); i++)

30             sum = max(sum, f1[i] + f2[i]);

31             

32         return sum;

33     }

34 };