122\. Best Time to Buy and Sell Stock II

Medium

You are given an integer array `prices` where `prices[i]` is the price of a given stock on the `ith` day.

On each day, you may decide to buy and/or sell the stock. You can only hold **at most one** share of the stock at any time. However, you can buy it then immediately sell it on the **same day**.

Find and return _the **maximum** profit you can achieve_.

**Example 1:**

**Input:** prices = [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. Total profit is 4 + 3 = 7. 

**Example 2:**

**Input:** prices = [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. Total profit is 4. 

**Example 3:**

**Input:** prices = [7,6,4,3,1]

**Output:** 0

**Explanation:** There is no way to make a positive profit, so we never buy the stock to achieve the maximum profit of 0. 

**Constraints:**

*   <code>1 <= prices.length <= 3 * 10<sup>4</sup></code>
*   <code>0 <= prices[i] <= 10<sup>4</sup></code>