leetcode: 5. 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:
#
# Input: "babad"
#
# Output: "bab"
#
# Note: "aba" is also a valid answer.
#
# Example:
#
# Input: "cbbd"
#
# Output: "bb"

class Solution():
    def longestPalindrome(self, s):
        if len(s) == 1:
            return s
        longest = ""
        for i in range(len(s)-1):
            tmp1 = self.longestPalindromeByAxis(s, i, i)
            longest = tmp1 if len(tmp1) > len(longest) else longest
            tmp2 = self.longestPalindromeByAxis(s, i, i+1)
            longest = tmp2 if len(tmp2) > len(longest) else longest
        return longest
    def longestPalindromeByAxis(self, s, left, right):
        while left >= 0 and right < len(s) and s[left] == s[right]:
            left, right = left - 1, right + 1
        return s[left + 1: right]


if __name__ == "__main__":
    assert Solution().longestPalindrome("a") == 'a'
    assert Solution().longestPalindrome("babad") == 'bab'
    assert Solution().longestPalindrome("cbbd") == 'bb'
    assert Solution().longestPalindrome("VABBCBBAS") == 'ABBCBBA'