<p>Given an integer <code>rowIndex</code>, return the <code>rowIndex<sup>th</sup></code> (<strong>0-indexed</strong>) row of the <strong>Pascal's triangle</strong>.</p> <p>In <strong>Pascal's triangle</strong>, each number is the sum of the two numbers directly above it as shown:</p> <img alt="" src="https://upload.wikimedia.org/wikipedia/commons/0/0d/PascalTriangleAnimated2.gif" style="height:240px; width:260px" /> <p> </p> <p><strong class="example">Example 1:</strong></p> <pre><strong>Input:</strong> rowIndex = 3 <strong>Output:</strong> [1,3,3,1] </pre><p><strong class="example">Example 2:</strong></p> <pre><strong>Input:</strong> rowIndex = 0 <strong>Output:</strong> [1] </pre><p><strong class="example">Example 3:</strong></p> <pre><strong>Input:</strong> rowIndex = 1 <strong>Output:</strong> [1,1] </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>0 <= rowIndex <= 33</code></li> </ul> <p> </p> <p><strong>Follow up:</strong> Could you optimize your algorithm to use only <code>O(rowIndex)</code> extra space?</p>