Best Time to Buy and Sell Stock II

You are given an integer array `prices` where `prices[i]` is the price of a given stock on the `i`th 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) then sell on day 3 (price = 5), profit = 5 - 1 = 4. Buy on day 4 (price = 3) then sell on day 5 (price = 6), profit = 6 - 3 = 3. Total profit = 4 + 3 = 7. ``` **Example 2:** ``` Input: prices = [1,2,3,4,5] Output: 4 Explanation: Buy on day 1 (price = 1) then 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 holding at most one share at a time. ``` **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. ```