Leetcode Best Time to Buy and Sell Stock III

Best Time to Buy and Sell Stock III

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).

1 两段分段思想
2 前往后，后往前都可以处理数列的思想

时间复杂度是O(n)，不掌握这种思想是很难做出来的。

class Solution {
public:
    int maxProfit(vector<int> &prices) 
	{
		vector<int> profit(prices.size()+1);

		int buy = INT_MAX;
		for (int i = 0; i < prices.size(); i++)
		{
			if (prices[i] < buy) buy = prices[i];
			else profit[i+1] = max(profit[i], prices[i]-buy);
		}

		int sale = INT_MIN , max_profit = 0, res = 0;
		for (int i = prices.size() - 1; i >= 0 ; i--)
		{
			if (prices[i] > sale) sale = prices[i];
			else max_profit = max(max_profit, sale - prices[i]);
			profit[i+1] = profit[i+1]+ max_profit;
			res = max(profit[i+1], res);
		}
		return res;
	}
};

Leetcode Best Time to Buy and Sell Stock III

原文：http://blog.csdn.net/kenden23/article/details/18156191