Say you have an array for which the ith element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete as many transactions as you like (i.e., buy one and sell one share of the stock multiple times).

Note: You may not engage in multiple transactions at the same time (i.e., you must sell the stock before you buy again).

Example 1:

Input: [7,1,5,3,6,4]
Output: 7
Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5), profit = 5-1 = 4.
             Then buy on day 4 (price = 3) and sell on day 5 (price = 6), profit = 6-3 = 3.

Example 2:

Input: [1,2,3,4,5]
Output: 4
Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.
             Note that you cannot buy on day 1, buy on day 2 and sell them later, as you are
             engaging multiple transactions at the same time. You must sell before buying again.

Example 3:

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

解題思路：區域性最優解即為全域性最優解，每次出現收益就累加收益，貪心。另外困難點可能在於沒有很強的能力將這個問題抽象到一個數學模型上，比如發生很多次買賣，當賣出時，同時可以再買入，這一步將問題抽象成了數學問題。

package tt;
import java.util.*;
public class TT {
    public static void main(String args[]) {
        int prices[]=new int[] {7,5,2,1,3,3,10,14};
        Solution test1=new Solution();
        System.out.println(test1.maxProfit(prices));
    }
}
class Solution {
    public int maxProfit(int[] prices) {
        int profit=0;
        for(int i=0;i<prices.length-1;i++) {
            if(prices[i+1]-prices[i]>0) {
                profit+=prices[i+1]-prices[i];
                }
            }
        return profit;
    }
}

Seen this question in a real interview before?