leetcode No121. Best Time to Buy and Sell Stock

Question：

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.

Example 1:

Input: [7, 1, 5, 3, 6, 4]Output: 5max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)

Example 2:

Input: [7, 6, 4, 3, 1]Output: 0In this case, no transaction is done, i.e. max profit = 0.

数组中的元素表示当天的股票价格，只允许一次买入卖出，求最大利润。

Algorithm：

遍历数组，更新最小值min，当天卖出的最大利润等于prices[i]-min，同时更新最大利润max。

Accepted Code：

class Solution {   //维护最小值和最大利润public:    int maxProfit(vector<int>& prices) {        if(prices.size()<2)return 0;        int min=prices[0];        int res=0;        for(int i=1;i<prices.size();i++)        {            if((prices[i]-min)>res)                res=prices[i]-min;            else if(prices[i]<min)                min=prices[i];        }        return res;    }};