Leetcode 121. Best Time to Buy and Sell Stock

题目：

Say you have an array for which the i^th element is the price of a given stock on dayi.

If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

思路：

动态规划法。从前向后遍历数组，记录当前出现过的最低价格，作为买入价格，并计算以当天价格出售的收益，作为可能的最大收益，整个遍历过程中，出现过的最大收益就是所求。

时间复杂度O（n）空间复杂度O（1）

代码：

C++实现：

class Solution {public:    int maxProfit(vector<int>& prices) {        int m = 65536 , s = 0;        for (int i = 0; i < prices.size(); i ++){            m = min(m, prices[i]);            s = max(s, prices[i] - m);        }        return s;    }};