Position of first occurrence

5. Position of first occurrence :
                                Given a text T and we receive request of the form : given a
   pattern P we need to know the position of first occurrence of P in T.
   To solve this we build the suffix automaton of the text T, we also need to add in the
   preprocessing finding fpos(first position of occurrence) for all states of automaton,
   such that
                               fpos[curr] = len[curr] - 1
                               fpos[clone] = fpos[q]
   then answer to our query is simply equal to fpos[t] - P.length() + 1,
   where, 't' is the state corresponding to pattern, P is the pattern.

st[curr].fpos = st[curr].len - 1;
st[clone].fpos = st[q].fpos;
at appropriate positions in sa_extend function.

int first_occurrene(string pattern)
{
    int ver = 0;
    int stat = 0;
    int len_P = pattern.length();
    while (st < len_P)
    {
        ver = st[ver].next[pattern[stat]-'a'];
        stat++;
    }
    return st[ver].fpos - len_P + 1;
}