题目：

题解：

char* shortestPalindrome(char* s) {int n = strlen(s);int fail[n + 1];memset(fail, -1, sizeof(fail));for (int i = 1; i < n; ++i) {int j = fail[i - 1];while (j != -1 && s[j + 1] != s[i]) {j = fail[j];}if (s[j + 1] == s[i]) {fail[i] = j + 1;}}int best = -1;for (int i = n - 1; i >= 0; --i) {while (best != -1 && s[best + 1] != s[i]) {best = fail[best];}if (s[best + 1] == s[i]) {++best;}}int ret_len = n - best - 1;char* ret = malloc(sizeof(char) * (ret_len + n + 1));for (int i = 0; i < ret_len; i++) ret[i] = s[n - i - 1];for (int i = 0; i < n; i++) ret[i + ret_len] = s[i];ret[ret_len + n] = 0;return ret;
}