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"

Solution: 

# @param {String} s
# @return {String}

def expand_around_center(s, left_idx, right_idx)
    while left_idx >= 0 && right_idx < s.length && s[left_idx] == s[right_idx]
        left_idx -= 1
        right_idx +=1
    end

    s[left_idx + 1...right_idx]
end

def longest_palindrome(s)
    return s if s.empty?

    longest = ""

    (0...s.length).each do |i|
        odd_palindrome = expand_around_center(s, i, i)
        even_palindrome = expand_around_center(s, i, i + 1)

        longest = odd_palindrome if longest.length < odd_palindrome.length
        longest = even_palindrome if longest.length < even_palindrome.length
    end

    longest
end