題目描述(Easy)

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).

題目連結

https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description/

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.

演算法分析

低進高出，把原始序列變為差分序列，把正的價格差價加起來。

提交程式碼：

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int sum = 0;
        for (int i = 1; i < prices.size(); ++i) {
            int diff = prices[i] - prices[i - 1];
            if (diff > 0) sum += diff;
        }
        
        return sum;
    }
};