LeetCode 121. Best Time to Buy and Sell Stock

这个题目很明显就是最好的买入卖出股票的时间，就是求一些列数中后面的数减去前面的数的最大值

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: 5

max. 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: 0

In this case, no transaction is done, i.e. max profit = 0.

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        size_t length = prices.size();
        if (!length)return 0;
        int profit = 0, minus = prices[0];
        for (int i = 1;i < length;++i)
        {
            if ((prices[i] - minus) > profit)
            {
                profit = prices[i] - minus;
                
            }
            if (minus > prices[i])minus = prices[i];
        }
        return profit;
    }
};