【Leetcode】Longest palindrome 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.

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写出来很简单，足够低的complexity通过LC却很难。直到看到这位大神的代码，简单清晰效率高，orz。

public class Solution {    int lo, maxLen;    public String longestPalindrome(String s) {    int len = s.length();    if (len < 2)        return s;    for (int i = 0; i < len-1; i++) {        extendPalindrome(s, i, i);  //assume odd length, try to extend Palindrome as possible        extendPalindrome(s, i, i+1); //assume even length.    }    return s.substring(lo, lo + maxLen);}private void extendPalindrome(String s, int j, int k) {    while (j >= 0 && k < s.length() && s.charAt(j) == s.charAt(k)) {        j--;        k++;    }    if (maxLen < k - j - 1) {        lo = j + 1;        maxLen = k - j - 1;    }}}