题目：

题解：

class Solution {public String shortestPalindrome(String s) {int n = s.length();int[] fail = new int[n];Arrays.fill(fail, -1);for (int i = 1; i < n; ++i) {int j = fail[i - 1];while (j != -1 && s.charAt(j + 1) != s.charAt(i)) {j = fail[j];}if (s.charAt(j + 1) == s.charAt(i)) {fail[i] = j + 1;}}int best = -1;for (int i = n - 1; i >= 0; --i) {while (best != -1 && s.charAt(best + 1) != s.charAt(i)) {best = fail[best];}if (s.charAt(best + 1) == s.charAt(i)) {++best;}}String add = (best == n - 1 ? "" : s.substring(best + 1));StringBuffer ans = new StringBuffer(add).reverse();ans.append(s);return ans.toString();}
}