*LeetCode-Best Time to Buy and Sell Stock

扫数组到当前这一天的时候，局部最优就是要么今天卖出（昨天不卖了）（前提是之前已经买了，且已知最大profit是在昨天卖出），要么今天买入（局部profit为零）

所以local的比较参数不是很好想明白。

public class Solution {    public int maxProfit(int[] prices) {        if (prices == null|| prices.length == 0 || prices.length == 1){            return 0;        }        int local = 0;        int global = 0;        for (int i = 0; i < prices.length-1; i ++){            local = Math.max(local + prices[i+1] - prices[i],0);            global = Math.max(local, global);        }        return global;    }}

另一种做法 不用dp 就找当前element之前的min price，然后维持max profit

public class Solution {    public int maxProfit(int[] prices) {        if (prices.length == 0)        {            return 0;        }        int max = 0, min = prices[0];        int profit = 0;        for (int i = 1; i < prices.length; i++)        {            if (prices[i] < min)            {                min = prices[i];            }            else            {                if (prices[i] - min > profit)                {                    profit = prices[i] - min;                }            }        }     return profit;    }}