Array - 122. Best Time to Buy and Sell Stock II

122. Best Time to Buy and Sell Stock II

Say you have an array for which the _i_th 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.

思路：

这道题使用暴力求解时间复杂度是O(n)，它和121题的区别是可以多次交易，于是可以转换为求所有价格上升的总盈利。使用贪心的思想求解。也可以寻找每一拐点，来累计总和。

代码：

java：

class Solution {

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