The best time to buy and sell stocks I leet code

Given an array, which i-th element is a given stock i-day prices.
If you are only allowed up to complete a transaction (ie buying and selling a stock), to design an algorithm to compute the maximum profit you can get.
Note that you can not sell the stock before buying stocks.
Example 1:

Example 1:

输入: [7,1,5,3,6,4]
输出: 5
解释: 在第 2 天（股票价格 = 1）的时候买入，在第 5 天（股票价格 = 6）的时候卖出，最大利润 = 6-1 = 5 。
     注意利润不能是 7-1 = 6, 因为卖出价格需要大于买入价格。

Example 2:

Example 1:

输入: [7,6,4,3,1]
输出: 0
解释: 在这种情况下, 没有交易完成, 所以最大利润为 0。

A Solution

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

Solution 2

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

Reproduced in: https: //www.jianshu.com/p/6433ba67bc91