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.

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"

public String longestPalindrome(String s) {
        if (s == null || s.length() <= 1) return s;
        final char[] chars = s.toCharArray();
        int len = 1;//回数长度
        int left = 0;
        int right = 0;
        for (int i = 0; i < chars.length; ++i) {
            for (int j = chars.length - 1; j > i; --j) {
                if ((j - i + 1) > len) {
                    if (isPalindrome(chars, i, j)) {
                        len = j - i + 1;
                        left = i;
                        right = j;
                    }
                } else {
                    break;
                }
            }
        }
        return s.substring(left, right + 1);
    }

  //判断是否是回数
   private boolean isPalindrome(char[] chars, int left, int right) {
        int i = left;
        int j = right;
        while (i < j) {
            if (chars[i++] != chars[j--]) {
                return false;
            }
        }
        return true;
    }