When cataloguing a collection of genetic strings, we should have an established system by which to organize
them. The standard method is to organize strings as they would appear in a dictionary, so that
"APPLE" precedes "APRON", which in turn comes before "ARMOR".
Problem
Assume that an alphabet$\mathscr{A}$ has a predetermined order;
that is, we write the alphabet as a permutation$\mathscr{A} = (a_1, a_2, \ldots, a_k)$,
where $a_1 < a_2 < \cdots < a_k$.
For instance, the English alphabet is organized as $(\textrm{A}, \textrm{B}, \ldots, \textrm{Z})$.
Given two strings $s$ and $t$ having the same length $n$,
we say that $s$ precedes $t$ in the lexicographic order (and write $s <_{\textrm{Lex}} t$) if the
first symbol $s[j]$ that doesn't match $t[j]$ satisfies $s_j < t_j$ in $\mathscr{A}$.
Given: A collection of at most 10 symbols defining an ordered alphabet, and a positive integer $n$ ($n \leq 10$).
Return: All strings of length $n$ that can be formed from the alphabet, ordered lexicographically (use the standard order of symbols in the English alphabet).
