longest-palindrome.js

/**
 *
 * @param {string} str
 * @returns {string}
 */
function longestPalindrome(str) {
  if (!str?.length) {
    return "";
  }

  let results = str[0];

  for (let i = 1; i < str.length; i++) {
    let char = str[i];
    let left = i;
    let right = i;
    while (left > 0 && str[left - 1] === char) {
      left--;
    }

    while (right < str.length && str[right + 1] === char) {
      right++;
      i++;
    }

    console.log("start left", left);
    
    while (
      left >= 0 &&
      right < str.length - 1 &&
      str[left - 1] === str[right + 1]
      ) {
        left--;
        right++;
    }

    if (results.length < right - left + 1) {
      results = str.slice(left, right + 1);
    }
  }

  return results;
}