leetcode--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, and there exists one unique longest palindromic substring.

public class Solution {
    public String longestPalindrome(String s) {
        if(s.length() < 2)
			return s;
		int len = s.length();
		String maxSub = "";
		int maxLen = 0;
		for(int i = 0; i < len; ++i){
			String tempOdd = expandPalindrome(s, i, i);
			if(maxLen < tempOdd.length()) {
				maxSub = tempOdd;
				maxLen = tempOdd.length();
			}
			
			if(i + 1 < len) {
				String tempEven = expandPalindrome(s, i , i + 1);
				if(maxLen < tempEven.length()) {
					maxSub = tempEven;
					maxLen = tempEven.length();
				}
			}
		}
		return maxSub;
    }
	
	private String expandPalindrome(String s, int left, int right){
		int len = s.length();
		while(left >= 0 && right < len && s.charAt(left) == s.charAt(right)) {
			--left;
			++right;
		}
		return s.substring(left + 1, right);
    }
}