最长回文子串长度

int len=strlen(s),id=0,maxlen=0;for(int i=len;i>=0;--i){    s[i+i+2]=s[i];    s[i+i+1]='#';}s[0]='*';for(int i=2;i<2*len+1;++i){    if(p[id]+id>i)p[i]=min(p[2*id-i],p[id]+id-i);    else p[i]=1;    while(s[i-p[i]] == s[i+p[i]])++p[i];    if(id+p[id]<i+p[i])id=i;    if(maxlen<p[i])maxlen=p[i];    }    printf("%d\n",maxlen-1);