<p>There are <code>n</code> different online courses numbered from <code>1</code> to <code>n</code>. You are given an array <code>courses</code> where <code>courses[i] = [duration<sub>i</sub>, lastDay<sub>i</sub>]</code> indicate that the <code>i<sup>th</sup></code> course should be taken <b>continuously</b> for <code>duration<sub>i</sub></code> days and must be finished before or on <code>lastDay<sub>i</sub></code>.</p> <p>You will start on the <code>1<sup>st</sup></code> day and you cannot take two or more courses simultaneously.</p> <p>Return <em>the maximum number of courses that you can take</em>.</p> <p> </p> <p><strong class="example">Example 1:</strong></p> <pre> <strong>Input:</strong> courses = [[100,200],[200,1300],[1000,1250],[2000,3200]] <strong>Output:</strong> 3 Explanation: There are totally 4 courses, but you can take 3 courses at most: First, take the 1<sup>st</sup> course, it costs 100 days so you will finish it on the 100<sup>th</sup> day, and ready to take the next course on the 101<sup>st</sup> day. Second, take the 3<sup>rd</sup> course, it costs 1000 days so you will finish it on the 1100<sup>th</sup> day, and ready to take the next course on the 1101<sup>st</sup> day. Third, take the 2<sup>nd</sup> course, it costs 200 days so you will finish it on the 1300<sup>th</sup> day. The 4<sup>th</sup> course cannot be taken now, since you will finish it on the 3300<sup>th</sup> day, which exceeds the closed date. </pre> <p><strong class="example">Example 2:</strong></p> <pre> <strong>Input:</strong> courses = [[1,2]] <strong>Output:</strong> 1 </pre> <p><strong class="example">Example 3:</strong></p> <pre> <strong>Input:</strong> courses = [[3,2],[4,3]] <strong>Output:</strong> 0 </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= courses.length <= 10<sup>4</sup></code></li> <li><code>1 <= duration<sub>i</sub>, lastDay<sub>i</sub> <= 10<sup>4</sup></code></li> </ul>