题目：

题解：

class Solution {public String longestPalindrome(String s) {int start = 0, end = -1;StringBuffer t = new StringBuffer("#");for (int i = 0; i < s.length(); ++i) {t.append(s.charAt(i));t.append('#');}t.append('#');s = t.toString();List<Integer> arm_len = new ArrayList<Integer>();int right = -1, j = -1;for (int i = 0; i < s.length(); ++i) {int cur_arm_len;if (right >= i) {int i_sym = j * 2 - i;int min_arm_len = Math.min(arm_len.get(i_sym), right - i);cur_arm_len = expand(s, i - min_arm_len, i + min_arm_len);} else {cur_arm_len = expand(s, i, i);}arm_len.add(cur_arm_len);if (i + cur_arm_len > right) {j = i;right = i + cur_arm_len;}if (cur_arm_len * 2 + 1 > end - start) {start = i - cur_arm_len;end = i + cur_arm_len;}}StringBuffer ans = new StringBuffer();for (int i = start; i <= end; ++i) {if (s.charAt(i) != '#') {ans.append(s.charAt(i));}}return ans.toString();}public int expand(String s, int left, int right) {while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {--left;++right;}return (right - left - 2) / 2;}
}