122、Best Time to Buy and Sell Stock II

Say you have an array for which the ithelement 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.

思路

无限次交易，得到最大的利润。遍历一遍，如果第二天比前一天价钱高，差价算入利润中，累积即可。

c++11

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

AC结果：

Runtime: 12 ms, faster than 21.83% of C++ online submissions for Best Time to Buy and Sell Stock II.
Memory Usage: 9.6 MB, less than 36.27% of C++ online submissions for Best Time to Buy and Sell Stock II.