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.

Solution：

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

(先贴代码，有空总结，DP 有意思)