<p>You are given an integer array <code>prices</code> where <code>prices[i]</code> is the price of a given stock on the <code>i<sup>th</sup></code> day.</p> <p>On each day, you may decide to buy and/or sell the stock. You can only hold <strong>at most one</strong> share of the stock at any time. However, you can buy it then immediately sell it on the <strong>same day</strong>.</p> <p>Find and return <em>the <strong>maximum</strong> profit you can achieve</em>.</p> <p> </p> <p><strong>Example 1:</strong></p> <pre> <strong>Input:</strong> prices = [7,1,5,3,6,4] <strong>Output:</strong> 7 <strong>Explanation:</strong> 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. </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> prices = [1,2,3,4,5] <strong>Output:</strong> 4 <strong>Explanation:</strong> Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4. Total profit is 4. </pre> <p><strong>Example 3:</strong></p> <pre> <strong>Input:</strong> prices = [7,6,4,3,1] <strong>Output:</strong> 0 <strong>Explanation:</strong> There is no way to make a positive profit, so we never buy the stock to achieve the maximum profit of 0. </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= prices.length <= 3 * 10<sup>4</sup></code></li> <li><code>0 <= prices[i] <= 10<sup>4</sup></code></li> </ul>