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.

思路保存当前最小值和当前最大收益，扫描更新。

class Solution {public:    int maxProfit(vector<int> &prices) {        if (prices.size() == 0) {            return 0;        }                int minValue = prices[0];        int maxProfit = 0;                for (int i = 0; i < prices.size(); i++) {            if (prices[i] < minValue) {                minValue = prices[i];             }                        if (prices[i] - minValue > maxProfit) {                maxProfit = prices[i] - minValue;            }        }                return maxProfit;    }};