5. Longest Palindromic Substring

https://leetcode.com/problems/longest-palindromic-substring/

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example 1:

Input: "babad" Output: "bab" Note: "aba" is also a valid answer.

Example 2:

Input: "cbbd" Output: "bb"