ps:題目來自力扣

最強回文子串

給你一個字符串?s，找到?s?中最長的?回文?子串。

class Solution {public String longestPalindrome(String s) {if (s == null || s.length() < 1) {return "";}int start = 0, end = 0;for (int i = 0; i < s.length(); i++) {// 以單個字符為中心擴展int len1 = expandAroundCenter(s, i, i);// 以兩個字符為中心擴展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) {while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {left--;right++;}return right - left - 1;}
}