https://leetcode.com/problems/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.