<p>Given a string <code>columnTitle</code> that represents the column title as appears in an Excel sheet, return <em>its corresponding column number</em>.</p> <p>For example:</p> <pre> A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... </pre> <p> </p> <p><strong class="example">Example 1:</strong></p> <pre> <strong>Input:</strong> columnTitle = "A" <strong>Output:</strong> 1 </pre> <p><strong class="example">Example 2:</strong></p> <pre> <strong>Input:</strong> columnTitle = "AB" <strong>Output:</strong> 28 </pre> <p><strong class="example">Example 3:</strong></p> <pre> <strong>Input:</strong> columnTitle = "ZY" <strong>Output:</strong> 701 </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= columnTitle.length <= 7</code></li> <li><code>columnTitle</code> consists only of uppercase English letters.</li> <li><code>columnTitle</code> is in the range <code>["A", "FXSHRXW"]</code>.</li> </ul>