<pre class="shiki github-dark shaku"><code>/** * @param {string} str * @return {number} */function countPalindromicSubstr(str) { // for a given index, return all possible palindromic substrings // of 2+ character length. function sweep(index) { let num = 0; let f; let b; // if current index and previous index are the same, that's a // 2-char palindrome f = str[index]; b = str[index - 1]; if (f &amp;&amp; b &amp;&amp; f === b) { num++; } // get 3+ char palindromes with char at index as center. // current distance out to check let distance = 0; let checking = true; while (checking) { distance++; f = str[index + distance]; b = str[index - distance]; if (f &amp;&amp; b &amp;&amp; f === b) { num++; } else { checking = false; } } return num; } // max length of palindromic substr let len = str.length; // now work our way up. if (len === 0) return 0; if (len === 1) return 1; // if length is 2 or more, we can sweep for palindromic substrings. // first, count each individual letter as a palindromic substring. let count = len; for (let i = 0; i &lt; len; i++) { count += sweep(i); } return count;}</code></pre>

Count palindromic substrings

A palindromic string reads the same backward as forward, such as 'madam'. Now given a string, count how many substrings it has? Like 'madam', it has f…