最长回文字符串

输入一个字符串，找出其中的最长的回文字符串，输入的都是字母。

#include <iostream>#include <cstring>#include <cstdio>#include <cstdlib>using namespace std;const int MAX = 1000010;char s[MAX];char ss[MAX<<1];int dp[MAX<<1];int solve(int len){    int ans = 0;    int right = -1;    int id = -1;    for(int i=0; i<len; i++)    {        int r = 1;        if(right >= i)            r = max(r, min(right-i+1, dp[2*id-i]));        while((i-r+1>=0&&i+r-1<len)&&(ss[i-r+1]==ss[i+r-1]))            r++;        r--;        if(i+r-1 > right)        {            right = i+r-1;            id = i;        }        dp[i] = r;        if(ans < r)            ans = r;    }    return ans - 1;}int main(){    int cas = 1;    while(scanf("%s", s) != EOF)    {        if(strcmp(s, "END") == 0)            break;        int len = strlen(s);        int cnt = 0;        for(int i=0; i<len; i++)        {            ss[cnt++] = '#';            ss[cnt++] = s[i];        }        ss[cnt++] = '#';        printf("%d\n",solve(cnt));    }    return 0;}