<p>You are given two strings <code>s</code> and <code>t</code>.</p> <p>String <code>t</code> is generated by random shuffling string <code>s</code> and then add one more letter at a random position.</p> <p>Return the letter that was added to <code>t</code>.</p> <p> </p> <p><strong>Example 1:</strong></p> <pre> <strong>Input:</strong> s = "abcd", t = "abcde" <strong>Output:</strong> "e" <strong>Explanation:</strong> 'e' is the letter that was added. </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> s = "", t = "y" <strong>Output:</strong> "y" </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>0 <= s.length <= 1000</code></li> <li><code>t.length == s.length + 1</code></li> <li><code>s</code> and <code>t</code> consist of lowercase English letters.</li> </ul>