Longest Palindromic Substring

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本文介绍了一种高效算法来找出给定字符串中的最长回文子串。通过分别查找奇数长度和偶数长度的回文子串，该算法能够确保找到唯一的最长回文子串。

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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.

Analysis: Find even and odd palindromic string separately.

public class Solution {
    public String helper(int left, int right, int size, String s) {
        while(left>=0 && right<=size-1) {
            if(s.charAt(left)!=s.charAt(right)) break;
            left--;
            right++;
        }
        return s.substring(left+1, right);
    }
    
    public String longestPalindrome(String s) {
        int size = s.length();
        if(size==0) return "";
        String res = "";
        
        // even palindrome
        for(int i=0; i<size; i++) {
            String temp1 = helper(i, i, size, s);
            if(temp1.length()>res.length()) res=temp1;
        }
        
        // odd palindrome
        for(int j=0; j<size-1; j++) {
            String temp2 = helper(j, j+1, size, s);
            if(temp2.length()>res.length()) res=temp2;
        }
        
        return res;
    }
}