<p>You are given two strings <code>s</code> and <code>t</code> consisting of only lowercase English letters.</p> <p>Return <em>the minimum number of characters that need to be appended to the end of </em><code>s</code><em> so that </em><code>t</code><em> becomes a <strong>subsequence</strong> of </em><code>s</code>.</p> <p>A <strong>subsequence</strong> is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.</p> <p> </p> <p><strong class="example">Example 1:</strong></p> <pre> <strong>Input:</strong> s = "coaching", t = "coding" <strong>Output:</strong> 4 <strong>Explanation:</strong> Append the characters "ding" to the end of s so that s = "coachingding". Now, t is a subsequence of s ("<u><strong>co</strong></u>aching<u><strong>ding</strong></u>"). It can be shown that appending any 3 characters to the end of s will never make t a subsequence. </pre> <p><strong class="example">Example 2:</strong></p> <pre> <strong>Input:</strong> s = "abcde", t = "a" <strong>Output:</strong> 0 <strong>Explanation:</strong> t is already a subsequence of s ("<u><strong>a</strong></u>bcde"). </pre> <p><strong class="example">Example 3:</strong></p> <pre> <strong>Input:</strong> s = "z", t = "abcde" <strong>Output:</strong> 5 <strong>Explanation:</strong> Append the characters "abcde" to the end of s so that s = "zabcde". Now, t is a subsequence of s ("z<u><strong>abcde</strong></u>"). It can be shown that appending any 4 characters to the end of s will never make t a subsequence. </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= s.length, t.length <= 10<sup>5</sup></code></li> <li><code>s</code> and <code>t</code> consist only of lowercase English letters.</li> </ul>