int Index_KMP(HString &S,HString &T,int pos)
{
    i=pos;
    j=1;
    while(i<=S.len&&j<=T.len)
    {
        if(S.ch[i]==T.ch[j])
        {
            ++i;
            ++j;
        }
        else j=next[j];
    }
    if(j>T.len) return i-T.len;
    else return 0;
}

里面的next[j]怎么编写?