解题思路：通过manachar算法求最长回文子串，如果用遍历的话绝对超时。

 

#include 
    
     #include 
     
      const int N = 220005;int rad[N];char string[N], tmpstr[N];int max(int a, int b) {    return a > b ? a : b;}int min(int a, int b) {    return a < b ? a : b;}int manachar() {    int ans = 0, mix = 0, id = 0, len = strlen(string);    for (int i = 1; i <= len; i++) {	if (mix > i)	    rad[i] = min(rad[2 * id - i], mix - i);	else	    rad[i] = 1;	for ( ; string[i - rad[i]] == string[i + rad[i]]; rad[i]++) {	    if (mix < i + rad[i]) {		mix = i + rad[i];		id = i;	    }	}	ans = max(ans, rad[i]);    }    return ans - 1;}int main() {    while (gets(tmpstr)) {	int len = strlen(tmpstr), cnt = 0;	string[cnt++] = '$';	for (int i = 0; i <= len; i++) {	    string[cnt++] = '#';	    string[cnt++] = tmpstr[i];	}	getchar();	printf("%d\n", manachar());    }    return 0;}