5. Longest Palindromic Substring Given a string s, return the longest palindromic substring in s. Example 1: Input: s = "babad" Output: "bab" Explanation: "aba" is also a valid answer. Example 2: Input: s = "cbbd" Output: "bb" Constraints: - 1 <= s.length <= 1000 - s consist of only digits and English letters.