Say you have an array for which the ith element is the price of a given stock on day i.

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.

分析：贪心算法。记录前面出现的price的最小值，然后用max(maxProfit, prices[i] - min)更新最大收益。代码如下：

class Solution {public:    int maxProfit(vector
     
       &prices) {        int maxPro = 0;        int minPri = INT_MAX;                for(int i = 0; i < prices.size(); i++){            if(prices[i] < minPri) minPri = prices[i];            else maxPro = max(maxPro, prices[i]-minPri);        }                return maxPro;    }};