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 1:

Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.
Example 2:

Input: "cbbd"
Output: "bb"

Java:

class Solution {
    public String longestPalindrome(String s) {
        int maxLength = 0;
        int b = 0, e = 0;
        char[] cs = s.toCharArray();
        for (int i = 0; i < cs.length-1; i++) {
            maxLength = Math.max(Math.max(helper(cs, i, i), helper(cs, i, i+1)), maxLength);
            if (e - b + 1 < maxLength) {
                b = i - maxLength / 2 + 1 - maxLength % 2;
                e = i + maxLength / 2;
            }
        }
        return s.substring(b, e+1);
    }
    
    private int helper(char[] cs, int i, int j) {
        int length = 0;
        while(i >= 0 && j < cs.length && cs[i] == cs[j]) {
            length = j - i + 1;
            i--;
            j++;
        }
        return length;
    }
}

Python:

class Solution:
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: str
        """
        res = ''
        for i, _ in enumerate(s):
            s1 = self.helper(s, i, i)
            s2 = self.helper(s, i, i+1) if i < len(s) - 1 else ''
            if len(res) <= len(s1):
                res = s1
            if len(res) <= len(s2):
                res = s2
                
        return res
    
    def helper(self, s, i, j):
        res = ''
        
        while i >= 0 and j < len(s) and s[i] == s[j]:
            res = s[i:j+1]
            i -= 1
            j += 1
        return res