005 Longest Palindromic Substring 最长回文子串

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"

详见：https://leetcode.com/problems/longest-palindromic-substring/description/

Java实现：

class Solution {
    public String longestPalindrome(String s) {
        int size=s.length();
        if(size==1||s.isEmpty()){
            return s;
        }
        int len=0;
        int start=0;
        int end=0;
        for(int i=0;i<size;++i){
            int len1=helper(s,i,i);
            int len2=helper(s,i,i+1);
            len=Math.max(len1,len2);
            if(len>(end-start)){
                start=i-(len-1)/2;
                end=i+(len/2);
            }
        }
        return s.substring(start,end+1);
    }
    private int helper(String s,int start,int end){
        while(start>=0&&end<s.length()&&s.charAt(start)==s.charAt(end)){
            --start;
            ++end;
        }
        return (end-start-1);
    }
}