Best Time to Buy and Sell Stock

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.

解题思路：

题意为给定股票每一个时间点的价格，且规定仅仅能买卖一次，问可以赚的最多的钱是多少。

记录当前为止最小的股价，然后当前股价与当前最小股价之差大于当前最大利润。则更新最大利润就可以。

class Solution {public:    int maxProfit(vector
     
      & prices) {        int len = prices.size();        if(len==0 || len==1){            return 0;        }        int maxProfit = 0;        int minPrices = prices[0];        for(int i=1; i