<p>The <strong>count-and-say</strong> sequence is a sequence of digit strings defined by the recursive formula:</p> <ul> <li><code>countAndSay(1) = "1"</code></li> <li><code>countAndSay(n)</code> is the way you would "say" the digit string from <code>countAndSay(n-1)</code>, which is then converted into a different digit string.</li> </ul> <p>To determine how you "say" a digit string, split it into the <strong>minimal</strong> number of substrings such that each substring contains exactly <strong>one</strong> unique digit. Then for each substring, say the number of digits, then say the digit. Finally, concatenate every said digit.</p> <p>For example, the saying and conversion for digit string <code>"3322251"</code>:</p> <img alt="" src="https://assets.leetcode.com/uploads/2020/10/23/countandsay.jpg" style="width: 581px; height: 172px;" /> <p>Given a positive integer <code>n</code>, return <em>the </em><code>n<sup>th</sup></code><em> term of the <strong>count-and-say</strong> sequence</em>.</p> <p> </p> <p><strong class="example">Example 1:</strong></p> <pre> <strong>Input:</strong> n = 1 <strong>Output:</strong> "1" <strong>Explanation:</strong> This is the base case. </pre> <p><strong class="example">Example 2:</strong></p> <pre> <strong>Input:</strong> n = 4 <strong>Output:</strong> "1211" <strong>Explanation:</strong> countAndSay(1) = "1" countAndSay(2) = say "1" = one 1 = "11" countAndSay(3) = say "11" = two 1's = "21" countAndSay(4) = say "21" = one 2 + one 1 = "12" + "11" = "1211" </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= n <= 30</code></li> </ul>