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.

Example:

Input: "babad"Output: "bab"Note: "aba" is also a valid answer.

Example:

Input: "cbbd"Output: "bb"

自己实现的代码

public static String longestPalindrome(String s) {String sb = s.substring(0, 1);int end = s.length();int j = 0;int i = 0;int begin = 1;while (end - begin > (sb.length() >> 1)) {i = j = begin;i--; j++;sb = assignMaxString(s, sb, end, j, i);i = j = begin++;i--;sb = assignMaxString(s, sb, end, j, i);}return sb;}private static String assignMaxString(String s, String sb, int end, int j, int i) {String s0 = null;if (j < end && s.charAt(i--) == s.charAt(j++)) {while (i > -1 && j < end && s.charAt(i) == s.charAt(j)) {i--; j++;};s0 = s.substring(i+1, j);if(sb.length() < s0.length()) {sb = s0;}}return sb;}

官方的代码:

public String longestPalindrome(String s) {    int start = 0, end = 0;    for (int i = 0; i < s.length(); i++) {        int len1 = expandAroundCenter(s, i, i);        int len2 = expandAroundCenter(s, i, i + 1);        int 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 expandAroundCenter(String s, int left, int right) {    int L = left, R = right;    while (L >= 0 && R < s.length() && s.charAt(L) == s.charAt(R)) {        L--;        R++;    }    return R - L - 1;}