5. Longest Palindromic Substring

Description:

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

　给定字符串，从中找出最长的回文串，假设最长不超过1000.

Example:

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

Input: "cbbd"
Output: "bb"

Solutions:

class Solution(object):
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: str
        """
        res = ""
        for i in range(len(s)):
            
            tmp = self.segment(s, i, i)
            if len(tmp) > len(res):
                res = tmp
                
            tmp = self.segment(s, i, i+1)
            if len(tmp) > len(res):
                res = tmp
        return res
              
    def segment(self, s, l, r):
        while l >= 0 and r < len(s) and s[l] == s[r]:
            l -= 1
            r += 1
        return s[l+1:r]